Endophytes have been demonstrated to trigger salicylic acid-dependent resistance and alter rhizosphere bacterial communities. However, few comprehensive studies have been conducted to elucidate the interactions between the direct (systemic resistance) and indirect (rhizosphere microbiome) defenses triggered by endophytes. The present study aimed to illuminate the possible roles of endophytic Bacillus megaterium in rice resistance against rice spikelet rot disease (SRD), and to make inferences on the potential interactions between plant defenses and the rhizosphere microenvironment. An outdoor pot experiment was conducted to explore the degree to which endophytes mitigate disease in rice, where four combination treatments were designed (inoculation and non-inoculation with B. megaterium, and infection with and without Fusarium proliferatum). Rice plants and rhizosphere soil, at the heading stage, were sampled to measure the accumulation of defense-related enzymes, including L-phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), β-1,3-glucanase and chitinase, and to perform 16S rRNA Illumina sequencing. Defense-related enzyme activities in rice plants inoculated with B. megaterium showed local or systemic increases. Plant-beneficial bacteria were found to be enriched when rice plants were treated with the endophyte. A correlation between plant resistance and the rhizosphere microbiome was also observed. The present study highlights the significance of B. megaterium for plant defenses against SRD through dual mechanism-systemic resistance and rhizosphere microbiome. Inferences of this study elucidate correlations between plant defenses and the rhizosphere microenvironment, which were attributed to the presence of B. megaterium.

The relevant research was published in the agroforestry science region 2 journal Applied Soil Ecology (SCI. (IF 3.445), with first author Cheng Ting, a master researcher in the College of Biological Sciences, and with Prof. Chuanchao Dai and Associate Prof. Wei He as co-corresponding authors. The research was financially supported by the National Key Research and Development Program of China (NO. 2017YFDO800705), and a project was funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions of China.