Fusarium verticillioides (Fv) is a mycotoxin-producing phytopathogen causing ear and root rot in maize. Bacillus cereus strain B25 is a maize endophyte and an effective biological control agent against Fv. The B25 genome contains several genes associated with fungal antagonism, including lytic enzymes (chitinases A and B, chitosanase and glycoside hydrolase), siderophores (petrobactin and bacillibactin), antibiotics (surfactin), and biofilm. This study aimed to elucidate which B25 antagonistic mechanisms are implicated in Fv biocontrol. The expression of twelve B25 genes was evaluated by qRT-PCR after 3–30 h of confrontation between B25 and Fv. All B25 genes tested were induced, mainly between 6 and 24 h, while none was induced at 3 h. Lytic enzyme genes were induced at different times, with three of them occurring at 12 h. Chitinase and chitosanase activities were induced after 6 and 12 h, respectively, and gradually increased until 30 h. Biofilm formation was detected only when B25 interacted with Fv. Images of the B25-Fv interaction and measurements at 24 and 30 h showed little branching or abnormal mycelial growth, suggesting cell wall damage. In conclusion, when B25 is confronted against Fv, all B25 antagonistic mechanisms tested appear to be involved in Fv growth control.

Maize chitinases are involved in chitin hydrolysis. Chitinases are distributed across various organisms including animals, plants, and fungi and are grouped into different glycosyl hydrolase families and classes, depending on protein structure. However, many chitinase functions and their interactions with other plant proteins remain unknown. The economic importance of maize (Zea mays L.) makes it relevant for studying the function of plant chitinases and their biological roles. This work aims to identify chitinase genes in the maize genome to study their gene structure, family/class classification, cis-related elements, and gene expression under biotic stress, such as Fusarium verticillioides infection. Thirty-nine chitinase genes were identified and found to be distributed in three glycosyl hydrolase (GH) families (18, 19 and 20). Likewise, the conserved domains and motifs were identified in each GH family member. The identified cis-regulatory elements are involved in plant development, hormone response, defense, and abiotic stress response. Chitinase protein-interaction network analysis predicted that they interact mainly with cell wall proteins. qRT-PCR analysis confirmed in silico data showing that ten different maize chitinase genes are induced in the presence of F. verticillioides, and that they could have several roles in pathogen infection depending on chitinase structure and cell wall localization.

Background: Maize in Mexico exhibits great genetic diversity, maintained by traditional practices of indigenous and non-indigenous communities, the same practices that have led to crop diversification over centuries. As one of the main staple crops worldwide, safeguarding the genetic diversity of maize is paramount to food security. Aims: This study evaluated the genetic diversity and population structure of traditionally cultured maize landraces in a rural seasonal agricultural community in Veracruz, Mexico, in order to learn how traditional practices shape these landraces, and propose strategies for their preservation. Methods: We analysed 118 individual maize samples belonging to five morphotypes (white, yellow, black, red and mottled) with eight microsatellite markers. Results: We encountered high genetic diversity, according to expected heterozygosity (H_e = 0.61). However, inbreeding coefficient and gene flow values suggested the existence of assortative mating, which causes low genetic differentiation. Population structure analysis identified three genetic pools, independent of grain colour. These findings suggest that all morphotypes belong to the same population, which is sub-structured due to assortative mating and gene flow related to local agronomic management. Conclusions: Current management practices in this community could lead to genetic erosion. In order to preserve diversity, wider regional seed exchange and selection for morphological diversity could be implemented.

One open question regarding plant–microbe interactions is how a plant interacts molecularly with both a beneficial microbe and a pathogenic fungus. This study used RNA-seq to investigate molecular responses in maize roots during a tripartite interaction with the fungal pathogen Fusarium verticillioides (Fv), which causes stalk, ear, and root rot, and the endophytic biocontrol agent Bacillus cereus sensu lato B25, known to suppress Fv and promote plant growth. Roots of seven-day-old maize inoculated with Fv (Zm-Fv), B25 (Zm-B25), and co-inoculated (Zm-Fv-B25) were compared to uninoculated control (Zm). Differential Gene Expression (DEG), Gene Ontology (GO) and KEGG analysis revealed distinct molecular responses. Fv suppressed plant pathways related to DNA and protein synthesis and impaired root development. In contrast, B25 triggered defense priming and growth-related responses. In the co-inoculation experiment (Zm-B25-Fv), upregulated DEGs were associated with both defense-related metabolic pathways, including jasmonic acid signaling and secondary metabolite biosynthesis, and genes involved in plant growth processes. Co-expression networks using Arabidopsis orthologs supported the induction of defense- and growth and development-related genes. This study is the first RNA-seq analysis of maize root molecular responses during the tripartite interaction with a fungal pathogen and its bacterial biocontrol agent, providing new directions for further research to understand the detailed molecular mechanisms underlying this interaction fully.

Background. Avocado (Persea americana) is a fruit crop of economic importance to Mexican agriculture which is experiencing increasing global demand. Consequently, the cultivated area and the use of chemical fertilizers have expanded. Agrochemicals can negatively affect soil health and reduce both the infectivity and effectiveness of arbuscular mycorrhizal fungi (AMF). Moreover, the composition of the AMF species may shift, favoring species adapted to high-disturbance conditions (ruderal strategy). Objective. To estimate the richness and abundance of AMF virtual taxa (VT, a proxy for “species”) in two avocado orchards differing in soil management practices. Methodology. Soil samples were collected from two orchards: Orchard 1 without agricultural management and, Orchard 2 with agricultural management. The soil was used to increase AMF propagules in trap plants and for physicochemical analyses. DNA was extracted from root segments and soil spores obtained from trap plants. Next, nested PCR using specific primers to amplify the Glomeromycota phylum was performed, then amplicons of ITS rDNA fragments were purified and sequencing in the Illumina MiSeq (2x300) platform. Results. A total of 29 virtual taxa were identified, 10 of which were resolved to species level, while the remaining fungal types belong to eight genera. 10 VT were shared between Orchards, six were exclusive to Orchard 1, and 13 to Orchard 2. However, in Orchard 1, 98.33% of the relative abundance was concentrated in only four VT, while in Orchard 2, three VT (98.51%) were dominated. Although richness (q = 0) was higher in Orchard 2 than in Orchard 1, the diversity indices of order 1 (q = 1) and 2 (q = 2) indicated no significant differences between orchards. Implications. This study suggests that agrochemicals may act as an environmental filter on AMF community assembly, favoring species with a ruderal strategy that translocate fewer nutrients to host plants. Additionally, new AMF species were recorded for Nayarit (Dominikia difficilevidera, Microkamienskia divaricate, and Orientoglomus emiratium). Conclusion. The use of agrochemicals alters the composition and abundance of AMF. Furthermore, molecular tools allowed us to increase the number of AMF species recorded in Nayarit.

One open question regarding plant-microbe interactions is how a plant interacts molecularly with both a beneficial microbe and a pathogenic fungus. This study used RNA-seq to investigate molecular responses in maize roots during a tripartite interaction with the fungal pathogen Fusarium verticillioides (Fv), which causes stalk, ear, and root rot, and the endophytic biocontrol agent Bacillus cereus sensu lato B25, known to suppress Fv and promote plant growth. Roots of seven-day-old maize inoculated with Fv (Zm-Fv), B25 (Zm-B25), and co-inoculated (Zm-Fv-B25) were compared to uninoculated control (Zm). Differential Gene Expression (DEG), Gene Ontology (GO) and KEGG analysis revealed distinct molecular responses. Fv suppressed plant pathways related to DNA and protein synthesis and impaired root development. In contrast, B25 triggered defense preparedness and growth-related responses. In the co-inoculation (Zm-Fv-B25), upregulated DEGs were associated with defense-related metabolic pathways, including jasmonic acid signaling and secondary metabolite biosynthesis, while also promoting plant growth. Co-expression networks using Arabidopsis orthologs supported these findings. This study is the first RNA-seq analysis of maize root molecular responses during the tripartite interaction with a fungal pathogen and its bacterial biocontrol agent, providing new directions for further research to understand the detailed molecular mechanisms underlying this interaction fully.