Abstract 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.

中文翻译：

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内生巨大芽孢杆菌触发水杨酸依赖性抗性并改善根际细菌群落以减轻水稻小穗腐烂病

摘要 内生菌已被证明可触发水杨酸依赖性抗性并改变根际细菌群落。然而，很少有综合研究来阐明由内生菌触发的直接（系统抗性）和间接（根际微生物组）防御之间的相互作用。本研究旨在阐明内生巨大芽孢杆菌在水稻抗水稻小穗腐烂病 (SRD) 中的可能作用，并推断植物防御与根际微环境之间的潜在相互作用。进行了户外盆栽试验以探索内生菌减轻水稻病害的程度，其中设计了四种组合处理（接种和不接种巨大芽孢杆菌、以及有和没有增殖镰刀菌的感染）。在抽穗期对水稻植株和根际土壤进行采样以测量防御相关酶的积累，包括 L-苯丙氨酸解氨酶 (PAL)、多酚氧化酶 (PPO)、β-1,3-葡聚糖酶和几丁质酶，并进行 16S rRNA Illumina 测序。接种巨大芽孢杆菌的水稻植株的防御相关酶活性显示出局部或全身性增加。当用内生菌处理水稻植株时，发现对植物有益的细菌富集。还观察到植物抗性与根际微生物组之间的相关性。本研究强调了巨大芽孢杆菌通过系统抗性和根际微生物群的双重机制对植物防御 SRD 的重要性。