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Dr. Harsh Bais
Associate Professor of Plant and Soil Interface, Department of Plant and Soil Sciences, University of Delaware, USA

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Preprint content
Published: 03 November 2020
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Rice (Oryza sativa) is a staple food crop worldwide and plays a critical role in ensuring food security as the global population continues to expand exponentially. Groundwater contamination with Arsenite [As(III)], a naturally occurring inorganic form of arsenic (As), leads to uptake and accumulation within rice plants. As a result, grain yield is lowered, the overall plant health is diminished, and there is a risk of arsenic toxicity from grain consumption. It was previously shown that a novel bacterial strain from the rice rhizosphere may reduce As accumulation in rice plants exposed to low levels of environmental As. We hypothesized that different rice varieties may exhibit varying responses to high As levels, resulting in differences in As uptake and toxicity. Utilizing the natural rice rhizospheric microbes, we initiated a set of hydroponic experiments with two rice varieties, Nipponbare (As tolerant) and IR66 (As susceptible). Rice varieties exposed to high As(III) concentration (50 uM) showed changes in both aboveground and belowground traits. As-tolerant Nipponbare varieties show grain production at high As(III) concentrations compared to the As-susceptible IR66 variety. Supplementation of natural rice rhizospheric microbes as single inoculums showed varied responses in both As-tolerant and As-susceptible varieties. Three natural rice rhizospheric microbes Pantoea sps (EA106), Pseudomonas corrugata (EA104), and Arthrobacter oxydans (EA201) were selected based on previously reported high Iron (Fe)-siderophore activity and were used for the hydroponic experiments as well as a non-rice rhizospheric strain, Bacillus subtilis UD1022. Interestingly, treatment with two strains (EA104 and EA201) led to a reduction in As(III) uptake in shoots, roots, and grains, and the degree of reduction of As(III) was pronounced in As-susceptible IR66 varieties. Non-rice rhizospheric UD1022 showed subtle protection against high As toxicity. High As(III) treatment led to a lack or delay of flowering and seed set in the As-susceptible IR66 variety. The data presented here may further the understanding of how beneficial microbes in the rhizosphere may help rice plants cope with high concentrations of As in the soil or groundwater.

ACS Style

Victoria Gundlah-Mooney; Harsh P. Bais. Rice rhizospheric microbes confer limited Arsenic protection under high Arsenic conditions. 2020, 1 .

AMA Style

Victoria Gundlah-Mooney, Harsh P. Bais. Rice rhizospheric microbes confer limited Arsenic protection under high Arsenic conditions. . 2020; ():1.

Chicago/Turabian Style

Victoria Gundlah-Mooney; Harsh P. Bais. 2020. "Rice rhizospheric microbes confer limited Arsenic protection under high Arsenic conditions." , no. : 1.

Original research article
Published: 03 April 2020 in Frontiers in Microbiology
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To establish host association, the innate immune system, which is one of the first lines of defense against infectious disease, must be circumvented. Plants encounter enteric foodborne bacterial pathogens under both pre- and post-harvest conditions. Human enteric foodborne pathogens can use plants as temporary hosts. This unique interaction may result in recalls and illness outbreaks associated with raw agricultural commodities. The purpose of this study was to determine if Salmonella enterica Typhimurium applied to lettuce leaves can suppress the innate stomatal defense in lettuce and utilization of UD1022 as a biocontrol against this ingression. Lettuce leaves were spot inoculated with S. Typhimurium wild type and its mutants. Bacterial culture and confocal microscopy analysis of stomatal apertures were used to support findings of differences in S. Typhimurium mutants compared to wild type. The persistence and internalization of these strains on lettuce was compared over a 7-day trial. S. Typhimurium may bypass the innate stomatal closure defense response in lettuce. Interestingly, a few key T3SS components in S. Typhimurium were involved in overriding stomatal defense response in lettuce for ingression. We also show that the T3SS in S. Typhimurium plays a critical role in persistence of S. Typhimurium in planta. Salmonella populations were significantly reduced in all UD1022 groups by day 7 with the exception of fliB and invA mutants. Salmonella internalization was not detected in plants after UD1022 treatment and had significantly higher stomatal closure rates (aperture width = 2.34 μm) by day 1 compared to controls (8.5 μm). S. Typhimurium SPI1 and SPI2 mutants showed inability to reopen stomates in lettuce suggesting the involvement of key T3SS components in suppression of innate response in plants. These findings impact issues of contamination related to plant performance and innate defense responses for plants.

ACS Style

Nicholas Johnson; Pushpinder Kaur Litt; Kalmia E. Kniel; Harsh Bais. Evasion of Plant Innate Defense Response by Salmonella on Lettuce. Frontiers in Microbiology 2020, 11, 500 .

AMA Style

Nicholas Johnson, Pushpinder Kaur Litt, Kalmia E. Kniel, Harsh Bais. Evasion of Plant Innate Defense Response by Salmonella on Lettuce. Frontiers in Microbiology. 2020; 11 ():500.

Chicago/Turabian Style

Nicholas Johnson; Pushpinder Kaur Litt; Kalmia E. Kniel; Harsh Bais. 2020. "Evasion of Plant Innate Defense Response by Salmonella on Lettuce." Frontiers in Microbiology 11, no. : 500.

Commentary
Published: 20 September 2018 in New Phytologist
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This article is a Commentary on Yang et al., 220: 567–578 .

ACS Style

Harsh P. Bais. We are family: kin recognition in crop plants. New Phytologist 2018, 220, 357 -359.

AMA Style

Harsh P. Bais. We are family: kin recognition in crop plants. New Phytologist. 2018; 220 (2):357-359.

Chicago/Turabian Style

Harsh P. Bais. 2018. "We are family: kin recognition in crop plants." New Phytologist 220, no. 2: 357-359.

Marschner review
Published: 21 May 2018 in Plant and Soil
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Our knowledge of plant beneficial bacteria in the rhizosphere is rapidly expanding due to intense interest in utilizing these types of microbes in agriculture. Laboratory and field studies consistently document the growth, health and protective benefits conferred to plants by applying plant growth promoting rhizobacteria (PGPR). PGPR exert their influence on other species, including plants, in the rhizosphere by producing a wide array of extracellular molecules for communication and defense. The types of PGPR molecular products are characteristically diverse, and the mechanisms by which they are acting on the plant are only beginning to be understood. While plants may contribute to shape their microbiome, it is these bacterial products which induce beneficial responses in plants. PGPR extracellular products can directly stimulate plant genetic and molecular pathways, leading to increases in plant growth and induction of plant resistance and tolerance. This review will discuss known PGPR-derived molecules, and how these products are implicated in inducing plant beneficial outcomes through complex plant response mechanisms. In order to move PGPR research to the next level, it will be important to describe and document the genetic and molecular mechanisms employed in these interactions. In this way, we will be able to restructure and harness these mechanisms in a way that allows for broad-based applications in agriculture. A greater depth of understanding of how these PGPR molecules are acting on the plant will allow more effective development of rhizobacterial applications in the field.

ACS Style

Amanda Rosier; Flávio H. V. Medeiros; Harsh P. Bais. Defining plant growth promoting rhizobacteria molecular and biochemical networks in beneficial plant-microbe interactions. Plant and Soil 2018, 428, 35 -55.

AMA Style

Amanda Rosier, Flávio H. V. Medeiros, Harsh P. Bais. Defining plant growth promoting rhizobacteria molecular and biochemical networks in beneficial plant-microbe interactions. Plant and Soil. 2018; 428 (1-2):35-55.

Chicago/Turabian Style

Amanda Rosier; Flávio H. V. Medeiros; Harsh P. Bais. 2018. "Defining plant growth promoting rhizobacteria molecular and biochemical networks in beneficial plant-microbe interactions." Plant and Soil 428, no. 1-2: 35-55.

Original research article
Published: 19 April 2017 in Frontiers in Plant Science
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When disrupted by stimuli such as herbivory, pathogenic infection, or mechanical wounding, plants secrete signals such as root exudates and volatile organic compounds (VOCs). The emission of VOCs induces a response in the neighboring plant communities and can improve plant fitness by alerting nearby plants of an impending threat and prompting them to alter their physiology for defensive purposes. In this study, we investigated the role of plant-derived signals, released as a result of mechanical wounding, that may play a role in intraspecific communication between Arabidopsis thaliana communities. Plant-derived signals released by the wounded plant resulted in more elaborate root development in the neighboring, unwounded plants. Such plant-derived signals also upregulated the Aluminum-activated malate transporter (ALMT1) responsible for the secretion of malic acid (MA) and the DR5 promoter, an auxin responsive promoter concentrated in root apex of the neighboring plants. We speculate that plant-derived signal-induced upregulation of root-specific ALMT1 in the undamaged neighboring plants sharing the environment with stressed plants may associate more with the benign microbes belowground. We also observed increased association of beneficial bacterium Bacillus subtilis UD1022 on roots of the neighboring plants sharing environment with the damaged plants. Wounding-induced plant-derived signals therefore induce defense mechanisms in the undamaged, local plants, eliciting a two-pronged preemptive response of more rapid root growth and up-regulation of ALMT1, resulting in increased association with beneficial microbiome.

ACS Style

Connor Sweeney; Venkatachalam Lakshmanan; Harsh P. Bais. Interplant Aboveground Signaling Prompts Upregulation of Auxin Promoter and Malate Transporter as Part of Defensive Response in the Neighboring Plants. Frontiers in Plant Science 2017, 8, 1 .

AMA Style

Connor Sweeney, Venkatachalam Lakshmanan, Harsh P. Bais. Interplant Aboveground Signaling Prompts Upregulation of Auxin Promoter and Malate Transporter as Part of Defensive Response in the Neighboring Plants. Frontiers in Plant Science. 2017; 8 ():1.

Chicago/Turabian Style

Connor Sweeney; Venkatachalam Lakshmanan; Harsh P. Bais. 2017. "Interplant Aboveground Signaling Prompts Upregulation of Auxin Promoter and Malate Transporter as Part of Defensive Response in the Neighboring Plants." Frontiers in Plant Science 8, no. : 1.

Original research article
Published: 13 October 2016 in Frontiers in Plant Science
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Our recent work has shown that a rice thizospheric natural isolate, a Pantoea sp (hereafter EA106) attenuates Arsenic (As) uptake in rice. In parallel, yet another natural rice rhizospheric isolate a Pseudomonas chlororaphis (hereafter EA105), was shown to inhibit rice blast pathogen Magnaporthe oryzae. Considering the above, we envisaged to evaluate the importance of mixed stress regime in rice plants subjected to both As toxicity and blast infections. Plants subjected to As regime showed increased susceptibility to blast infections compared to As-untreated plants. Rice blast pathogen M. oryzae showed significant resistance against As toxicity compared to other non-host fungal pathogens. Interestingly, plants treated with EA106 showed reduced susceptibility against blast infections in plants pre-treated with As. This data also corresponded with lower As uptake in plants primed with EA106. In addition, we also evaluated the expression of defense related genes in host plants subjected to As treatment. The data showed that plants primed with EA106 upregulated defense-related genes with or without As treatment. The data shows the first evidence of how rice plants cope with mixed stress regimes. Our work highlights the importance of natural association of plant microbiome which determines the efficacy of benign microbes to promote the development of beneficial traits in plants.

ACS Style

Venkatachalam Lakshmanan; Jonathon Cottone; Harsh P. Bais. Killing Two Birds with One Stone: Natural Rice Rhizospheric Microbes Reduce Arsenic Uptake and Blast Infections in Rice. Frontiers in Plant Science 2016, 7, 1 .

AMA Style

Venkatachalam Lakshmanan, Jonathon Cottone, Harsh P. Bais. Killing Two Birds with One Stone: Natural Rice Rhizospheric Microbes Reduce Arsenic Uptake and Blast Infections in Rice. Frontiers in Plant Science. 2016; 7 ():1.

Chicago/Turabian Style

Venkatachalam Lakshmanan; Jonathon Cottone; Harsh P. Bais. 2016. "Killing Two Birds with One Stone: Natural Rice Rhizospheric Microbes Reduce Arsenic Uptake and Blast Infections in Rice." Frontiers in Plant Science 7, no. : 1.

Review
Published: 20 January 2016 in Plant Molecular Biology
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Recent work has shown that the rhizospheric and phyllospheric microbiomes of plants are composed of highly diverse microbial species. Though the information pertaining to the diversity of the aboveground and belowground microbes associated with plants is known, an understanding of the mechanisms by which these diverse microbes function is still in its infancy. Plants are sessile organisms, that depend upon chemical signals to interact with the microbiota. Of late, the studies related to the impact of microbes on plants have gained much traction in the research literature, supporting diverse functional roles of microbes on plant health. However, how these microbes interact as a community to confer beneficial traits to plants is still poorly understood. Recent advances in the use of “biologicals” as bio-fertilizers and biocontrol agents for sustainable agricultural practices is promising, and a fundamental understanding of how microbes in community work on plants could help this approach be more successful. This review attempts to highlight the importance of different signaling events that mediate a beneficial plant microbe interaction. Fundamental research is needed to understand how plants react to different benign microbes and how these microbes are interacting with each other. This review highlights the importance of chemical signaling, and biochemical and genetic events which determine the efficacy of benign microbes to promote the development of beneficial traits in plants.

ACS Style

Amanda Rosier; Usha Bishnoi; Venkatachalam Lakshmanan; D. Janine Sherrier; Harsh P. Bais. A perspective on inter-kingdom signaling in plant–beneficial microbe interactions. Plant Molecular Biology 2016, 90, 537 -548.

AMA Style

Amanda Rosier, Usha Bishnoi, Venkatachalam Lakshmanan, D. Janine Sherrier, Harsh P. Bais. A perspective on inter-kingdom signaling in plant–beneficial microbe interactions. Plant Molecular Biology. 2016; 90 (6):537-548.

Chicago/Turabian Style

Amanda Rosier; Usha Bishnoi; Venkatachalam Lakshmanan; D. Janine Sherrier; Harsh P. Bais. 2016. "A perspective on inter-kingdom signaling in plant–beneficial microbe interactions." Plant Molecular Biology 90, no. 6: 537-548.

Original research article
Published: 01 December 2015 in Frontiers in Plant Science
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Rice suffers dramatic yield losses due to blast pathogen Magnaporthe oryzae. Pseudomonas chlororaphis EA105, a bacterium that was isolated from the rice rhizosphere, inhibits M. oryzae. It was shown previously that pre-treatment of rice with EA105 reduced the size of blast lesions through JA- and ETH-mediated ISR. ABA acts antagonistically towards SA, JA, and ETH signaling, to impede plant defense responses. EA105 may be reducing the virulence of M. oryzae by preventing the pathogen from up-regulating the key ABA biosynthetic gene NCED3 in rice roots, as well as a β-glucosidase likely involved in activating conjugated inactive forms of ABA. However, changes in total ABA concentrations were not apparent, provoking the question of whether ABA concentration is an indicator of ABA signaling and response. In the rice-M. oryzae interaction, ABA plays a dual role in disease severity by increasing plant susceptibility and accelerating pathogenesis in the fungus itself. ABA is biosynthesized by M. oryzae. Further, exogenous ABA increased spore germination and appressoria formation, distinct from other plant growth regulators. EA105, which inhibits appressoria formation, counteracted the virulence-promoting effects of ABA on M. oryzae. The role of endogenous fungal ABA in blast disease was confirmed through the inability of a knockout mutant impaired in ABA biosynthesis to form lesions on rice. Therefore, it appears that EA105 is invoking multiple strategies in its protection of rice from blast including direct mechanisms as well as those mediated through plant signaling. ABA is a molecule that is likely implicated in both tactics.

ACS Style

Carla A. Spence; Venkatachalam Lakshmanan; Nicole Donofrio; Harsh P. Bais. Crucial Roles of Abscisic Acid Biogenesis in Virulence of Rice Blast Fungus Magnaporthe oryzae. Frontiers in Plant Science 2015, 6, 1 .

AMA Style

Carla A. Spence, Venkatachalam Lakshmanan, Nicole Donofrio, Harsh P. Bais. Crucial Roles of Abscisic Acid Biogenesis in Virulence of Rice Blast Fungus Magnaporthe oryzae. Frontiers in Plant Science. 2015; 6 ():1.

Chicago/Turabian Style

Carla A. Spence; Venkatachalam Lakshmanan; Nicole Donofrio; Harsh P. Bais. 2015. "Crucial Roles of Abscisic Acid Biogenesis in Virulence of Rice Blast Fungus Magnaporthe oryzae." Frontiers in Plant Science 6, no. : 1.

Journal article
Published: 27 August 2015 in Genome Announcements
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Bacillus subtilis , which belongs to the phylum Firmicutes , is the most widely studied Gram-positive model organism. It is found in a wide variety of environments and is particularly abundant in soils and in the gastrointestinal tracts of ruminants and humans. Here, we present the complete genome sequence of the newly described B. subtilis strain UD1022. The UD1022 genome consists of a 4.025-Mbp chromosome, and other major findings from our analysis will provide insights into the genomic basis of it being a plant growth-promoting rhizobacterium (PGPR) with biocontrol potential.

ACS Style

Usha Bishnoi; Shawn W. Polson; D. Janine Sherrier; Harsh P. Bais. Draft Genome Sequence of a Natural Root Isolate, Bacillus subtilis UD1022, a Potential Plant Growth-Promoting Biocontrol Agent. Genome Announcements 2015, 3, e00696-15 .

AMA Style

Usha Bishnoi, Shawn W. Polson, D. Janine Sherrier, Harsh P. Bais. Draft Genome Sequence of a Natural Root Isolate, Bacillus subtilis UD1022, a Potential Plant Growth-Promoting Biocontrol Agent. Genome Announcements. 2015; 3 (4):e00696-15.

Chicago/Turabian Style

Usha Bishnoi; Shawn W. Polson; D. Janine Sherrier; Harsh P. Bais. 2015. "Draft Genome Sequence of a Natural Root Isolate, Bacillus subtilis UD1022, a Potential Plant Growth-Promoting Biocontrol Agent." Genome Announcements 3, no. 4: e00696-15.

Review article
Published: 27 June 2015 in Current Opinion in Plant Biology
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Growth regulators act not only as chemicals that modulate plant growth but they also act as signal molecules under various biotic and abiotic stresses. Of all growth regulators, abscisic acid (ABA) is long known for its role in modulating plants response against both biotic and abiotic stress. Although the genetic information for ABA biosynthesis in plants is well documented, the knowledge about ABA biosynthesis in other organisms is still in its infancy. It is known that various microbes including bacteria produce and secrete ABA, but the overall functional significance of why ABA is synthesized by microbes is not known. Here we discuss the functional involvement of ABA biosynthesis by a pathogenic fungus. Furthermore, we propose that ABA biosynthesis in plant pathogenic fungi could be targeted for novel fungicidal discovery.

ACS Style

Carla Spence; Harsh Bais. Role of plant growth regulators as chemical signals in plant–microbe interactions: a double edged sword. Current Opinion in Plant Biology 2015, 27, 52 -58.

AMA Style

Carla Spence, Harsh Bais. Role of plant growth regulators as chemical signals in plant–microbe interactions: a double edged sword. Current Opinion in Plant Biology. 2015; 27 ():52-58.

Chicago/Turabian Style

Carla Spence; Harsh Bais. 2015. "Role of plant growth regulators as chemical signals in plant–microbe interactions: a double edged sword." Current Opinion in Plant Biology 27, no. : 52-58.

Journal article
Published: 10 June 2015 in Planta
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A natural rice rhizospheric isolate abates arsenic uptake in rice by increasing Fe plaque formation on rice roots. Rice (Oryza sativa L.) is the staple food for over half of the world’s population, but its quality and yield are impacted by arsenic (As) in some regions of the world. Bacterial inoculants may be able to mitigate the negative impacts of arsenic assimilation in rice, and we identified a nonpathogenic, naturally occurring rice rhizospheric bacterium that decreases As accumulation in rice shoots in laboratory experiments. We isolated several proteobacterial strains from a rice rhizosphere that promote rice growth and enhance the oxidizing environment surrounding rice root. One Pantoea sp. strain (EA106) also demonstrated increased iron (Fe)-siderophore in culture. We evaluated EA106’s ability to impact rice growth in the presence of arsenic, by inoculation of plants with EA106 (or control), subsequently grew the plants in As-supplemented medium, and quantified the resulting plant biomass, Fe and As concentrations, localization of Fe and As, and Fe plaque formation in EA106-treated and control plants. These results show that both arsenic and iron concentrations in rice can be altered by inoculation with the soil microbe EA106. The enhanced accumulation of Fe in the roots and in root plaques suggests that EA106 inoculation improves Fe uptake by the root and promotes the formation of a more oxidative environment in the rhizosphere, thereby allowing more expansive plaque formation. Therefore, this microbe may have the potential to increase food quality through a reduction in accumulation of toxic As species within the aerial portions of the plant.

ACS Style

Venkatachalam Lakshmanan; Deepak Shantharaj; Gang Li; Angelia L. Seyfferth; D. Janine Sherrier; Harsh P. Bais. A natural rice rhizospheric bacterium abates arsenic accumulation in rice (Oryza sativa L.). Planta 2015, 242, 1037 -1050.

AMA Style

Venkatachalam Lakshmanan, Deepak Shantharaj, Gang Li, Angelia L. Seyfferth, D. Janine Sherrier, Harsh P. Bais. A natural rice rhizospheric bacterium abates arsenic accumulation in rice (Oryza sativa L.). Planta. 2015; 242 (4):1037-1050.

Chicago/Turabian Style

Venkatachalam Lakshmanan; Deepak Shantharaj; Gang Li; Angelia L. Seyfferth; D. Janine Sherrier; Harsh P. Bais. 2015. "A natural rice rhizospheric bacterium abates arsenic accumulation in rice (Oryza sativa L.)." Planta 242, no. 4: 1037-1050.

Feature
Published: 01 October 2014 in The Biochemist
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Plants are stationary organisms, generally restricted to one location for the duration of their growth and development, which is why the need for clear means of information exchange becomes paramount. Above-ground, plants readily emit pungent volatile substances to signal danger of eminent attack to their relatives or to attract the enemy of their enemies. However, most plant communication is occurring below the ground, where plants are secreting compounds from their roots to send messages to neighbouring plants, microbes and insects in the rhizosphere. Although we think of plants as silent and autonomous, they are actually having very complex and specific conversations to communicate with kin, shape their microbiome, and deter invasive plants and pathogens from taking up residence. Rather than blindly fumbling through the soil matrix in hopes of encountering the conditions for ideal growth, plant roots are actively exploring and modulating their surroundings. Root communication is not only critical in terms of an individual plant's success, but it is becoming clear that this activity has consequences to plant populations at the community and ecosystem scale. This article discusses belowground plant communication via root secretion and the resulting ecological significance.

ACS Style

Amanda Roberson; Carla Spence; Harsh P. Bais. Underground communication: Belowground signalling mediates diverse root–root and root–microbe interactions. The Biochemist 2014, 36, 32 -35.

AMA Style

Amanda Roberson, Carla Spence, Harsh P. Bais. Underground communication: Belowground signalling mediates diverse root–root and root–microbe interactions. The Biochemist. 2014; 36 (5):32-35.

Chicago/Turabian Style

Amanda Roberson; Carla Spence; Harsh P. Bais. 2014. "Underground communication: Belowground signalling mediates diverse root–root and root–microbe interactions." The Biochemist 36, no. 5: 32-35.

Journal article
Published: 24 July 2014 in Plant Physiology
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There is considerable evidence in the literature that beneficial rhizospheric microbes can alter plant morphology, enhance plant growth, and increase mineral content. Of late, there is a surge to understand the impact of the microbiome on plant health. Recent research shows the utilization of novel sequencing techniques to identify the microbiome in model systems such as Arabidopsis (Arabidopsis thaliana) and maize (Zea mays). However, it is not known how the community of microbes identified may play a role to improve plant health and fitness. There are very few detailed studies with isolated beneficial microbes showing the importance of the functional microbiome in plant fitness and disease protection. Some recent work on the cultivated microbiome in rice (Oryza sativa) shows that a wide diversity of bacterial species is associated with the roots of field-grown rice plants. However, the biological significance and potential effects of the microbiome on the host plants are completely unknown. Work performed with isolated strains showed various genetic pathways that are involved in the recognition of host-specific factors that play roles in beneficial host-microbe interactions. The composition of the microbiome in plants is dynamic and controlled by multiple factors. In the case of the rhizosphere, temperature, pH, and the presence of chemical signals from bacteria, plants, and nematodes all shape the environment and influence which organisms will flourish. This provides a basis for plants and their microbiomes to selectively associate with one another. This Update addresses the importance of the functional microbiome to identify phenotypes that may provide a sustainable and effective strategy to increase crop yield and food security.

ACS Style

Venkatachalam Lakshmanan; Gopinath Selvaraj; Harsh P. Bais. Functional Soil Microbiome: Belowground Solutions to an Aboveground Problem. Plant Physiology 2014, 166, 689 -700.

AMA Style

Venkatachalam Lakshmanan, Gopinath Selvaraj, Harsh P. Bais. Functional Soil Microbiome: Belowground Solutions to an Aboveground Problem. Plant Physiology. 2014; 166 (2):689-700.

Chicago/Turabian Style

Venkatachalam Lakshmanan; Gopinath Selvaraj; Harsh P. Bais. 2014. "Functional Soil Microbiome: Belowground Solutions to an Aboveground Problem." Plant Physiology 166, no. 2: 689-700.

Journal article
Published: 01 January 2014 in BMC Plant Biology
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The natural interactions between plant roots and their rhizospheric microbiome are vital to plant fitness, modulating both growth promotion and disease suppression. In rice (Oryza sativa), a globally important food crop, as much as 30% of yields are lost due to blast disease caused by fungal pathogen Magnaporthe oryzae. Capitalizing on the abilities of naturally occurring rice soil bacteria to reduce M. oryzae infections could provide a sustainable solution to reduce the amount of crops lost to blast disease. Naturally occurring root-associated rhizospheric bacteria were isolated from California field grown rice plants (M-104), eleven of which were taxonomically identified by 16S rRNA gene sequencing and fatty acid methyl ester (FAME) analysis. Bacterial isolates were tested for biocontrol activity against the devastating foliar rice fungal pathogen, M. oryzae pathovar 70-15. In vitro, a Pseudomonas isolate, EA105, displayed antibiosis through reducing appressoria formation by nearly 90% as well as directly inhibiting fungal growth by 76%. Although hydrogen cyanide (HCN) is a volatile commonly produced by biocontrol pseudomonads, the activity of EA105 seems to be independent of its HCN production. During in planta experiments, EA105 reduced the number of blast lesions formed by 33% and Pantoea agglomerans isolate, EA106 by 46%. Our data also show both EA105 and EA106 trigger jasmonic acid (JA) and ethylene (ET) dependent induced systemic resistance (ISR) response in rice. Out of 11 bacteria isolated from rice soil, pseudomonad EA105 most effectively inhibited the growth and appressoria formation of M. oryzae through a mechanism that is independent of cyanide production. In addition to direct antagonism, EA105 also appears to trigger ISR in rice plants through a mechanism that is dependent on JA and ET signaling, ultimately resulting in fewer blast lesions. The application of native bacteria as biocontrol agents in combination with current disease protection strategies could aid in global food security.

ACS Style

Carla Spence; Emily Alff; Cameron Johnson; Cassandra Ramos; Nicole Donofrio; Venkatesan Sundaresan; Harsh Bais. Natural rice rhizospheric microbes suppress rice blast infections. BMC Plant Biology 2014, 14, 130 -130.

AMA Style

Carla Spence, Emily Alff, Cameron Johnson, Cassandra Ramos, Nicole Donofrio, Venkatesan Sundaresan, Harsh Bais. Natural rice rhizospheric microbes suppress rice blast infections. BMC Plant Biology. 2014; 14 (1):130-130.

Chicago/Turabian Style

Carla Spence; Emily Alff; Cameron Johnson; Cassandra Ramos; Nicole Donofrio; Venkatesan Sundaresan; Harsh Bais. 2014. "Natural rice rhizospheric microbes suppress rice blast infections." BMC Plant Biology 14, no. 1: 130-130.

Journal article
Published: 23 June 2013 in Planta
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Our previous work has demonstrated that Arabidopsis thaliana can actively recruit beneficial rhizobacteria Bacillus subtilis strain FB17 (hereafter FB17) through an unknown shoot-to-root long-distance signaling pathway post a foliar bacterial pathogen attack. However, it is still not well understood which genetic targets FB17 affects in plants. Microarray analysis of A. thaliana roots treated with FB17 post 24 h of treatment showed 168 and 129 genes that were up- and down-regulated, respectively, compared with the untreated control roots. Those up-regulated include auxin-regulated genes as well as genes involved in metabolism, stress response, and plant defense. In addition, other defense-related genes, as well as cell-wall modification genes were also down-regulated with FB17 colonization. Expression patterns of 20 selected genes were analyzed by semi-quantitative RT-PCR, validating the microarray results. A. thaliana insertion mutants were used against FB17 to further study the functional response of the differentially expressed genes. Five mutants for the up-regulated genes were tested for FB17 colonization, three (at3g28360, at3g20190 and at1g21240) mutants showed decreased FB17 colonization on the roots while increased FB17 titers was seen with three mutants of the down-regulated genes (at3g27980, at4g19690 and at5g56320). Further, these mutants for up-regulated genes and down-regulated genes were foliar infected with Pseudomonas syringae pv. tomato (hereafter PstDC3000) and analyzed for Aluminum activated malate transporter (ALMT1) expression which showed that ALMT1 may be the key regulator for root FB17 colonization. Our microarray showed that under natural condition, FB17 triggers plant responses in a manner similar to known plant growth-promoting rhizobacteria and to some extent also suppresses defense-related genes expression in roots, enabling stable colonization. The possible implication of this study opens up a new dialogin terms of how beneficial microbes regulate plant genetic response for mutualistic associations.

ACS Style

Venkatachalam Lakshmanan; Rafael Castaneda; Thimmaraju Rudrappa; Harsh P. Bais. Root transcriptome analysis of Arabidopsis thaliana exposed to beneficial Bacillus subtilis FB17 rhizobacteria revealed genes for bacterial recruitment and plant defense independent of malate efflux. Planta 2013, 238, 657 -668.

AMA Style

Venkatachalam Lakshmanan, Rafael Castaneda, Thimmaraju Rudrappa, Harsh P. Bais. Root transcriptome analysis of Arabidopsis thaliana exposed to beneficial Bacillus subtilis FB17 rhizobacteria revealed genes for bacterial recruitment and plant defense independent of malate efflux. Planta. 2013; 238 (4):657-668.

Chicago/Turabian Style

Venkatachalam Lakshmanan; Rafael Castaneda; Thimmaraju Rudrappa; Harsh P. Bais. 2013. "Root transcriptome analysis of Arabidopsis thaliana exposed to beneficial Bacillus subtilis FB17 rhizobacteria revealed genes for bacterial recruitment and plant defense independent of malate efflux." Planta 238, no. 4: 657-668.

Book chapter
Published: 18 March 2013 in Molecular Microbial Ecology of the Rhizosphere
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ACS Style

Meredith L. Biedrzycki; Harsh P. Bais. Root Secretions: Interrelating Genes and Molecules to Microbial Associations. Is it All that Simple? Molecular Microbial Ecology of the Rhizosphere 2013, 137 -140.

AMA Style

Meredith L. Biedrzycki, Harsh P. Bais. Root Secretions: Interrelating Genes and Molecules to Microbial Associations. Is it All that Simple? Molecular Microbial Ecology of the Rhizosphere. 2013; ():137-140.

Chicago/Turabian Style

Meredith L. Biedrzycki; Harsh P. Bais. 2013. "Root Secretions: Interrelating Genes and Molecules to Microbial Associations. Is it All that Simple?" Molecular Microbial Ecology of the Rhizosphere , no. : 137-140.

Journal article
Published: 01 March 2013 in Journal of Biological Chemistry
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Mitochondria are important targets of metal toxicity and are also vital for maintaining metal homeostasis. Here, we examined the potential role of mitochondria in homeostasis of nickel in the roots of nickel hyperaccumulator plant Alyssum murale. We evaluated the biochemical basis of nickel tolerance by comparing the role of mitochondria in closely related nickel hyperaccumulator A. murale and non-accumulator Alyssum montanum. Evidence is presented for the rapid and transient influx of nickel in root mitochondria of nickel hyperaccumulator A. murale. In an early response to nickel treatment, substantial nickel influx was observed in mitochondria prior to sequestration in vacuoles in the roots of hyperaccumulator A. murale compared with non-accumulator A. montanum. In addition, the mitochondrial Krebs cycle was modulated to increase synthesis of malic acid and citric acid involvement in nickel hyperaccumulation. Furthermore, malic acid, which is reported to form a complex with nickel in hyperaccumulators, was also found to reduce the reactive oxygen species generation induced by nickel. We propose that the interaction of nickel with mitochondria is imperative in the early steps of nickel uptake in nickel hyperaccumulator plants. Initial uptake of nickel in roots results in biochemical responses in the root mitochondria indicating its vital role in homeostasis of nickel ions in hyperaccumulation.

ACS Style

Bhavana Agrawal; Kirk Czymmek; Donald L. Sparks; Harsh P. Bais. Transient Influx of Nickel in Root Mitochondria Modulates Organic Acid and Reactive Oxygen Species Production in Nickel Hyperaccumulator Alyssum murale. Journal of Biological Chemistry 2013, 288, 7351 -7362.

AMA Style

Bhavana Agrawal, Kirk Czymmek, Donald L. Sparks, Harsh P. Bais. Transient Influx of Nickel in Root Mitochondria Modulates Organic Acid and Reactive Oxygen Species Production in Nickel Hyperaccumulator Alyssum murale. Journal of Biological Chemistry. 2013; 288 (10):7351-7362.

Chicago/Turabian Style

Bhavana Agrawal; Kirk Czymmek; Donald L. Sparks; Harsh P. Bais. 2013. "Transient Influx of Nickel in Root Mitochondria Modulates Organic Acid and Reactive Oxygen Species Production in Nickel Hyperaccumulator Alyssum murale." Journal of Biological Chemistry 288, no. 10: 7351-7362.

Review
Published: 01 December 2012 in Plant Signaling & Behavior
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Often, plant-pathogenic microbe interactions are discussed in a host-microbe two-component system, however very little is known about how the diversity of rhizospheric microbes that associate with plants affect host performance against pathogens. There are various studies, which specially direct the importance of induced systemic defense (ISR) response in plants interacting with beneficial rhizobacteria, yet we don't know how rhizobacterial associations modulate plant physiology. In here, we highlight the many dimensions within which plant roots associate with beneficial microbes by regulating aboveground physiology. We review approaches to study the causes and consequences of plant root association with beneficial microbes on aboveground plant-pathogen interactions. The review provides the foundations for future investigations into the impact of the root beneficial microbial associations on plant performance and innate defense responses.

ACS Style

Amutha Sampath Kumar; Harsh P. Bais. Wired to the roots. Plant Signaling & Behavior 2012, 7, 1598 -1604.

AMA Style

Amutha Sampath Kumar, Harsh P. Bais. Wired to the roots. Plant Signaling & Behavior. 2012; 7 (12):1598-1604.

Chicago/Turabian Style

Amutha Sampath Kumar; Harsh P. Bais. 2012. "Wired to the roots." Plant Signaling & Behavior 7, no. 12: 1598-1604.

Journal article
Published: 24 September 2012 in The Plant Journal
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Plants exist in a complex multitrophic environment, where they interact with and compete for resources with other plants, microbes and animals. Plants have a complex array of defense mechanisms, such as the cell wall being covered with a waxy cuticle serving as a potent physical barrier. Although some pathogenic fungi infect plants by penetrating through the cell wall, many bacterial pathogens invade plants primarily through stomata on the leaf surface. Entry of the foliar pathogen, Pseudomonas syringae pathovar tomato DC3000 (hereafter PstDC3000), into the plant corpus occurs through stomatal openings, and consequently a key plant innate immune response is the transient closure of stomata, which delays disease progression. Here, we present evidence that the root colonization of the rhizobacteria Bacillus subtilis FB17 (hereafter FB17) restricts the stomata‐mediated pathogen entry of PstDC3000 in Arabidopsis thaliana. Root binding of FB17 invokes abscisic acid (ABA) and salicylic acid (SA) signaling pathways to close light‐adapted stomata. These results emphasize the importance of rhizospheric processes and environmental conditions as an integral part of the plant innate immune system against foliar bacterial infections.

ACS Style

Amutha Sampath Kumar; Venkatachalam Lakshmanan; Jeffrey L. Caplan; Deborah Powell; Kirk Czymmek; Delphis F. Levia; Harsh P. Bais. RhizobacteriaBacillus subtilisrestricts foliar pathogen entry through stomata. The Plant Journal 2012, 72, 694 -706.

AMA Style

Amutha Sampath Kumar, Venkatachalam Lakshmanan, Jeffrey L. Caplan, Deborah Powell, Kirk Czymmek, Delphis F. Levia, Harsh P. Bais. RhizobacteriaBacillus subtilisrestricts foliar pathogen entry through stomata. The Plant Journal. 2012; 72 (4):694-706.

Chicago/Turabian Style

Amutha Sampath Kumar; Venkatachalam Lakshmanan; Jeffrey L. Caplan; Deborah Powell; Kirk Czymmek; Delphis F. Levia; Harsh P. Bais. 2012. "RhizobacteriaBacillus subtilisrestricts foliar pathogen entry through stomata." The Plant Journal 72, no. 4: 694-706.

Journal article
Published: 12 September 2012 in Plant Physiology
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This study demonstrated that foliar infection by Pseudomonas syringae pv tomato DC3000 induced malic acid (MA) transporter (ALUMINUM-ACTIVATED MALATE TRANSPORTER1 [ALMT1]) expression leading to increased MA titers in the rhizosphere of Arabidopsis (Arabidopsis thaliana). MA secretion in the rhizosphere increased beneficial rhizobacteria Bacillus subtilis FB17 (hereafter FB17) titers causing an induced systemic resistance response in plants against P. syringae pv tomato DC3000. Having shown that a live pathogen could induce an intraplant signal from shoot-to-root to recruit FB17 belowground, we hypothesized that pathogen-derived microbe-associated molecular patterns (MAMPs) may relay a similar response specific to FB17 recruitment. The involvement of MAMPs in triggering plant innate immune response is well studied in the plant’s response against foliar pathogens. In contrast, MAMPs-elicited plant responses on the roots and the belowground microbial community are not well understood. It is known that pathogen-derived MAMPs suppress the root immune responses, which may facilitate pathogenicity. Plants subjected to known MAMPs such as a flagellar peptide, flagellin22 (flg22), and a pathogen-derived phytotoxin, coronatine (COR), induced a shoot-to-root signal regulating ALMT1 for recruitment of FB17. Micrografts using either a COR-insensitive mutant (coi1) or a flagellin-insensitive mutant (fls2) as the scion and ALMT1pro:β-glucuronidase as the rootstock revealed that both COR and flg22 are required for a graft transmissible signal to recruit FB17 belowground. The data suggest that MAMPs-induced signaling to regulate ALMT1 is salicylic acid and JASMONIC ACID RESISTANT1 (JAR1)/JASMONATE INSENSITIVE1 (JIN1)/MYC2 independent. Interestingly, a cell culture filtrate of FB17 suppressed flg22-induced MAMPs-activated root defense responses, which are similar to suppression of COR-mediated MAMPs-activated root defense, revealing a diffusible bacterial component that may regulate plant immune responses. Further analysis showed that the biofilm formation in B. subtilis negates suppression of MAMPs-activated defense responses in roots. Moreover, B. subtilis suppression of MAMPs-activated root defense does require JAR1/JIN1/MYC2. The ability of FB17 to block the MAMPs-elicited signaling pathways related to antibiosis reflects a strategy adapted by FB17 for efficient root colonization. These experiments demonstrate a remarkable strategy adapted by beneficial rhizobacteria to suppress a host defense response, which may facilitate rhizobacterial colonization and host-mutualistic association.

ACS Style

Venkatachalam Lakshmanan; Sherry L. Kitto; Jeffrey L. Caplan; Yi-Huang Hsueh; Daniel Kearns; Yu-Sung Wu; Harsh P. Bais. Microbe-Associated Molecular Patterns-Triggered Root Responses Mediate Beneficial Rhizobacterial Recruitment in Arabidopsis. Plant Physiology 2012, 160, 1642 -1661.

AMA Style

Venkatachalam Lakshmanan, Sherry L. Kitto, Jeffrey L. Caplan, Yi-Huang Hsueh, Daniel Kearns, Yu-Sung Wu, Harsh P. Bais. Microbe-Associated Molecular Patterns-Triggered Root Responses Mediate Beneficial Rhizobacterial Recruitment in Arabidopsis. Plant Physiology. 2012; 160 (3):1642-1661.

Chicago/Turabian Style

Venkatachalam Lakshmanan; Sherry L. Kitto; Jeffrey L. Caplan; Yi-Huang Hsueh; Daniel Kearns; Yu-Sung Wu; Harsh P. Bais. 2012. "Microbe-Associated Molecular Patterns-Triggered Root Responses Mediate Beneficial Rhizobacterial Recruitment in Arabidopsis." Plant Physiology 160, no. 3: 1642-1661.