New Insights on Endophytic Microbacterium-Assisted Blast Disease Suppression and Growth Promotion in Rice: Revelation by Polyphasic Functional Characterization and Transcriptomics

Abstract

Plant growth-promoting endophytic microbes have drawn the attention of researchers owing to their ability to confer fitness benefits in many plant species. Here, we report agriculturally beneficial traits of rice-leaf-adapted endophytic <i>Microbacterium testaceum</i>. Our polyphasic taxonomic investigations revealed its identity as <i>M. testaceum</i>. The bacterium displayed typical endophytism in rice leaves, indicated by the green fluorescence of GFP-tagged <i>M. testaceum in</i> confocal laser scanning microscopy. Furthermore, the bacterium showed mineral solubilization and production of IAA, ammonia, and hydrolytic enzymes. Tobacco leaf infiltration assay confirmed its non-pathogenic nature on plants. The bacterium showed antifungal activity on <i>Magnaporthe oryzae</i>, as exemplified by secreted and volatile organic metabolome-mediated mycelial growth inhibition. GC-MS analysis of the volatilome of <i>M. testaceum</i> indicated the abundance of antimicrobial compounds. Bacterization of rice seedlings showed phenotypic traits of MAMP-triggered immunity (MTI), over-expression of <i>OsNPR1</i> and <i>OsCERK</i>, and the consequent blast suppressive activity. Strikingly, <i>M. testaceum</i> induced the transcriptional tradeoff between physiological growth and host defense pathways as indicated by up- and downregulated DEGs. Coupled with its plant probiotic features and the defense elicitation activity, the present study paves the way for developing <i>Microbacterium testaceum-</i>mediated bioformulation for sustainably managing rice blast disease.