The plant microbiota consists of a multitude of microorganisms that can affect plant health and fitness. However, it is currently unclear how the plant shapes its leaf microbiota and what role the plant immune system plays in this process. Here, we evaluated Arabidopsis thaliana mutants with defects in different parts of the immune system for an altered bacterial community assembly using a gnotobiotic system. While higher-order mutants in receptors that recognize microbial features and in defence hormone signalling showed substantial microbial community alterations, the absence of the plant NADPH oxidase RBOHD caused the most pronounced change in the composition of the leaf microbiota. The rbohD knockout resulted in an enrichment of specific bacteria. Among these, we identified Xanthomonas strains as opportunistic pathogens that colonized wild-type plants asymptomatically but caused disease in rbohD knockout plants. Strain dropout experiments revealed that the lack of RBOHD unlocks the pathogenicity of individual microbiota members driving dysbiosis in rbohD knockout plants. For full protection, healthy plants require both a functional immune system and a microbial community. Our results show that the NADPH oxidase RBOHD is essential for microbiota homeostasis and emphasizes the importance of the plant immune system in controlling the leaf microbiota.

植物微生物群由大量可影响植物健康和适应性的微生物组成。然而，目前尚不清楚植物如何塑造其叶片微生物群以及植物免疫系统在这一过程中扮演什么角色。在这里，我们评估了在免疫系统不同部分存在缺陷的拟南芥突变体，以使用无菌系统改变细菌群落组装。虽然识别微生物特征和防御激素信号的受体中的高阶突变体显示出显着的微生物群落变化，但植物 NADPH 氧化酶 RBOHD 的缺失导致叶片微生物群组成发生最显着的变化。rbohD敲除导致特定细菌的富集。其中，我们确定作为机会性病原体的黄单胞菌菌株无症状地定植于野生型植物，但在rbohD基因敲除植物中引起疾病​​。菌株脱落实验表明，缺乏 RBOHD 会释放个体微生物群成员的致病性，从而导致rbohD基因敲除植物的生态失调。为了获得全面保护，健康的植物需要功能性免疫系统和微生物群落。我们的研究结果表明，NADPH 氧化酶 RBOHD 对于微生物群稳态至关重要，并强调了植物免疫系统在控制叶片微生物群中的重要性。