Commensal lifestyle regulated by a negative feedback loop betweenArabidopsisROS and the bacterial T2SS

Abstract

AbstractDespite the plant health-promoting effects of plant microbiota, these assemblages also comprise potentially detrimental microbes. How plant immunity controls its microbiota to promote plant health under these conditions remains largely unknown. We found that commensal bacteria isolated from healthyArabidopsisplants trigger diverse patterns of reactive oxygen species (ROS) production via the NADPH oxidase RBOHD that selectively inhibited specific commensals, notablyXanthomonasL148. Through random mutagenesis, we found that L148gspE, encoding a type II secretion system (T2SS) component, is required for the damaging effects ofXanthomonasL148 onrbohDmutant plants.In plantabacterial transcriptomics revealed that RBOHD suppresses most T2SS gene expression includinggspE. L148 colonization protected plants against a bacterial pathogen, whengspEwas inhibited by ROS or mutation. Thus, a negative feedback loop betweenArabidopsisROS and the bacterial T2SS tames a potentially detrimental leaf commensal and turns it into a microbe beneficial to the host.