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.

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.

Maize is a major global crop; however, its production is affected by Fusarium verticillioides, which causes stalk, ear, and root rot. Bacillus cereus B25 is a maize bacterium that antagonizes F. verticillioides, likely through antifungal compounds and possibly by inducing maize chitinase genes. Fusarium verticillioides effectively infects maize by producing a chitinase-modifying protein that disrupts maize chitinases, preventing fungal cell wall degradation and evasion of plant immune responses triggered by Pathogen-Associated Molecular Patterns. The aim of this work was to analyze maize, B25, and F. verticillioides gene expression during bipartite and tripartite interactions at early stages (5, 7, 10, and 14 days post-inoculation). Physiological results showed increased root and shoot growth in maize seedlings under the tripartite interactions compared to fungus alone. B25 was demonstrated to grow endophytically and coexist with F. verticillioides in maize roots. Maize extracellular chitinase genes were induced, possibly due to chitin fragments released from the fungal cell wall, while the fungus effector genes were also upregulated in response. Furthermore, the chitinase gene Zm00001eb317090 (bk4) may contribute to cell wall strengthening, as suggested by in silico co-expression analyses. Overall, these results support a coordinated interaction between maize and B25 that contributes to controlling F. verticillioides infection.

Plant growth-promoting rhizobacteria (PGPR) offer a sustainable alternative to mitigate the excessive use of synthetic agrochemicals in modern agriculture. This study focused on the isolation and molecular characterization of endophytic bacteria from jalapeño pepper ( Capsicum annuum L.) to evaluate their multi-functional PGPR traits and antagonistic activity against phytopathogenic fungi. Phylogenetic analysis identified several genera, including Stenotrophomonas, Pseudomonas, Paenibacillus, Klebsiella, Aeromonas, and Enterobacter. Among these, Klebsiella IR6 and Enterobacter IR9 significantly enhanced vegetative vigor under greenhouse conditions compared to the untreated control. These isolates demonstrated robust phosphate solubilization, siderophore production, and in vitro antagonism against Fusarium oxysporum (15%–34% growth inhibition). Furthermore, endophytic colonization of the root tissues by Klebsiella IR6 was successfully validated via confocal scanning microscopy using green fluorescent protein-tagged cells transformed with the pAD4325 plasmid. These findings suggest that Enterobacter and Klebsiella isolates are promising biotechnological tools for optimizing horticultural yields, while reducing chemical dependence. Nevertheless, further field evaluations across diverse jalapeño hybrids are essential to validate the consistency and stability of both as reliable bio-inoculants for sustainable agriculture.

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.