Synergistic consortium of beneficial microorganisms in rice rhizosphere promotes host defense to blight-causing Xanthomonas oryzae pv. oryzae.

Abstract

Rice plants primed with beneficial microbes Bacillus amyloliquefaciens and Aspergillus spinulosporus with biocontrol potential against Xanthomonas oryzae pv. oryzae, provided protection from disease by reprogramming host defence response under pathogen challenge. Plant-beneficial microbe interactions taking place in the rhizosphere are widely used for growth promotion and mitigation of biotic stresses in plants. The present study aims to evaluate the defense network induced by beneficial microorganisms in the rice rhizosphere, and the three-way interaction involved upon inoculation with dreadful bacteria Xanthomonas oryzae pv. oryzae (Xoo). Differential expression of defense-related enzymes, proteins, and genes in rice variety Swarna primed with a microbial consortium of Bacillus amyloliquefaciens and Aspergillus spinulosporus were quantified in the presence and absence of Xoo. The time-based expression profile alterations in leaves under the five distinct treatments "(unprimed unchallenged, unprimed Xoo challenged, B. amyloliquefaciens primed and challenged, A. spinulosporus primed and challenged, B. amyloliquefaciens and A. spinulosporus consortium primed and challenged)" revealed differential early upregulation of SOD, PAL, PO, PPO activities and TPC content in beneficial microbes primed plants in comparison to unprimed challenged plants. The enhanced defense response in all the rice plants recruited with beneficial microbe was also reflected by reduced plant mortality and an increased plant dry biomass and chlorophyll content. Also, more than 550 protein spots were observed per gel by PD Quest software, a total of 55 differentially expressed protein spots were analysed used MALDI-TOF MS, out of which 48 spots were recognized with a significant score with direct or supporting roles in stress alleviation and disease resistance. qRT-PCR was carried out to compare the biochemical and proteomic data to mRNA levels. We conclude that protein biogenesis and alleviated resistance response may contribute to improved biotic stress adaptation. These results might accelerate the functional regulation of the Xoo-receptive proteins in the presence of beneficial rhizospheric microbes and their computation as promising molecular markers for superior disease management.