AP2/ERF–type transcription factors regulate important functions of plant growth and development as well as responses to environmental stimuli. A rice AP2/ERF transcription factor, OsEREBP1 is a downstream component of a signal transduction pathway in a specific interaction between rice (Oryza sativa) and its bacterial pathogen, Xoo (Xanthomonas oryzae pv. oryzae). Constitutive expression of OsEREBP1 in rice driven by maize ubiquitin promoter did not affect normal plant growth. Microarray analysis revealed that over expression of OsEREBP1 caused increased expression of lipid metabolism related genes such as lipase and chloroplastic lipoxygenase as well as several genes related to jasmonate and abscisic acid biosynthesis. PR genes, transcription regulators and Aldhs (alcohol dehydrogenases) implicated in abiotic stress and submergence tolerance were also upregulated in transgenic plants. Transgenic plants showed increase in endogenous levels of α-linolenate, several jasmonate derivatives and abscisic acid but not salicylic acid. Soluble modified GFP (SmGFP)-tagged OsEREBP1 was localized to plastid nucleoids. Comparative analysis of non-transgenic and OsEREBP1 overexpressing genotypes revealed that OsEREBP1 attenuates disease caused by Xoo and confers drought and submergence tolerance in transgenic rice. Our results suggest that constitutive expression of OsEREBP1 activates the jasmonate and abscisic acid signalling pathways thereby priming the rice plants for enhanced survival under abiotic or biotic stress conditions. OsEREBP1 is thus, a good candidate gene for engineering plants for multiple stress tolerance.

The polyadenylation of mRNA is one of the critical processing steps during expression of almost all eukaryotic genes. It is tightly integrated with transcription, particularly its termination, as well as other RNA processing events, i.e. capping and splicing. The poly(A) tail protects the mRNA from unregulated degradation, and it is required for nuclear export and translation initiation. In recent years, it has been demonstrated that the polyadenylation process is also involved in the regulation of gene expression. The polyadenylation process requires two components, the cis-elements on the mRNA and a group of protein factors that recognize the cis-elements and produce the poly(A) tail. Here we report a comprehensive pairwise protein-protein interaction mapping and gene expression profiling of the mRNA polyadenylation protein machinery in Arabidopsis.

As in other cereal crops, the panicles of sorghum (Sorghum bicolor (L.) Moench) comprise two types of floral spikelets (grass flowers). Only sessile spikelets (SSs) are capable of producing viable grains, whereas pedicellate spikelets (PSs) cease development after initiation and eventually abort. Consequently, grain number per panicle (GNP) is lower than the total number of flowers produced per panicle. The mechanism underlying this differential fertility is not well understood. To investigate this issue, we isolated a series of ethyl methane sulfonate (EMS)-induced multiseeded (msd) mutants that result in full spikelet fertility, effectively doubling GNP. Previously, we showed that MSD1 is a TCP (Teosinte branched/Cycloidea/PCF) transcription factor that regulates jasmonic acid (JA) biosynthesis, and ultimately floral sex organ development. Here, we show that MSD2 encodes a lipoxygenase (LOX) that catalyzes the first committed step of JA biosynthesis. Further, we demonstrate that MSD1 binds to the promoters of MSD2 and other JA pathway genes. Together, these results show that a JA-induced module regulates sorghum panicle development and spikelet fertility. The findings advance our understanding of inflorescence development and could lead to new strategies for increasing GNP and grain yield in sorghum and other cereal crops.

Aflatoxin contamination is a global menace that adversely affects food crops and human health. Peanut seed coat is the outer layer protecting the cotyledon both at pre- and post-harvest stages from biotic and abiotic stresses. The aim of the present study is to investigate the role of seed coat against A. flavus infection. In-vitro seed colonization (IVSC) with and without seed coat showed that the seed coat acts as a physical barrier, and the developmental series of peanut seed coat showed the formation of a robust multilayered protective seed coat. Radial growth bioassay revealed that both insoluble and soluble seed coat extracts from 55-437 line (resistant) showed higher A. flavus inhibition compared to TMV-2 line (susceptible). Further analysis of seed coat biochemicals showed that hydroxycinnamic and hydroxybenzoic acid derivatives are the predominant phenolic compounds, and addition of these compounds to the media inhibited A. flavus growth. Gene expression analysis showed that genes involved in lignin monomer, proanthocyanidin, and flavonoid biosynthesis are highly abundant in 55-437 compared to TMV-2 seed coats. Overall, the present study showed that the seed coat acts as a physical and biochemical barrier against A. flavus infection and its potential use in mitigating the aflatoxin contamination.

Grain number per panicle is an important component of grain yield in sorghum (Sorghum bicolor (L.)) and other cereal crops. Previously, we reported that mutations in multi-seeded 1 (MSD1) and MSD2 genes result in a two-fold increase in grain number per panicle due to the restoration of the fertility of the pedicellate spikelets, which invariably abort in natural sorghum accessions. Here, we report the identification of another gene, MSD3, which is also involved in the regulation of grain numbers in sorghum. Four bulked F₂ populations from crosses between BTx623 and each of the independent msd mutants p6, p14, p21, and p24 were sequenced to 20× coverage of the whole genome on a HiSeq 2000 system. Bioinformatic analyses of the sequence data showed that one gene, Sorbi_3001G407600, harbored homozygous mutations in all four populations. This gene encodes a plastidial ω-3 fatty acid desaturase that catalyzes the conversion of linoleic acid (18:2) to linolenic acid (18:3), a substrate for jasmonic acid (JA) biosynthesis. The msd3 mutants had reduced levels of linolenic acid in both leaves and developing panicles that in turn decreased the levels of JA. Furthermore, the msd3 panicle phenotype was reversed by treatment with methyl-JA (MeJA). Our characterization of MSD1, MSD2, and now MSD3 demonstrates that JA-regulated processes are critical to the msd phenotype. The identification of the MSD3 gene reveals a new target that could be manipulated to increase grain number per panicle in sorghum, and potentially other cereal crops, through the genomic editing of MSD3 functional orthologs.

Main conclusion: A novel inducible secretion system mutation in Sorghum named Red root has been identified. The mutant plant root exudes pigmented compounds that enriches Actinobacteria in its rhizosphere compared to BTx623. Favorable plant–microbe interactions in the rhizosphere positively influence plant growth and stress tolerance. Sorghum bicolor, a staple biomass and food crop, has been shown to selectively recruit Gram-positive bacteria (Actinobacteria) in its rhizosphere under drought conditions to enhance stress tolerance. However, the genetic/biochemical mechanism underlying the selective enrichment of specific microbial phyla in the sorghum rhizosphere is poorly known due to the lack of available mutants with altered root secretion systems. Using a subset of sorghum ethyl methanesulfonate (EMS) mutant lines, we have isolated a novel Red root (RR) mutant with an increased accumulation and secretion of phenolic compounds in roots. Genetic analysis showed that RR is a single dominant mutation. We further investigated the effect of root-specific phenolic compounds on rhizosphere microbiome composition under well-watered and water-deficit conditions. The microbiome diversity analysis of the RR rhizosphere showed that Actinobacteria were enriched significantly under the well-watered condition but showed no significant change under the water-deficit condition. BTx623 rhizosphere showed a significant increase in Actinobacteria under the water-deficit condition. Overall, the rhizosphere of RR genotype retained a higher bacterial diversity and richness relative to the rhizosphere of BTx623, especially under water-deficit condition. Therefore, the RR mutant provides an excellent genetic resource for rhizosphere-microbiome interaction studies as well as to develop drought-tolerant lines. Identification of the RR gene and the molecular mechanism through which the mutant selectively enriches microbial populations in the rhizosphere will be useful in designing strategies for improving sorghum productivity and stress tolerance.