Commensal lifestyle regulated by a negative feedback loop between Arabidopsis ROS and the bacterial T2SS

Area of Science:

• Plant-microbe interactions
• Plant immunity
• Microbial pathogenesis

Background:

• Plant microbiota can contain both beneficial and detrimental microbes.
• Mechanisms by which plant immunity selectively controls its microbiota are largely unknown.

Purpose of the Study:

• To investigate how plant immunity, specifically reactive oxygen species (ROS) production, shapes the plant microbiota.
• To understand the role of the NADPH oxidase RBOHD in controlling commensal bacteria.

Main Methods:

• Isolation and characterization of commensal bacteria from Arabidopsis plants.
• Analysis of ROS production patterns triggered by commensal bacteria.
• Random mutagenesis of Xanthomonas L148 to identify genes involved in pathogenicity.
• In planta bacterial transcriptomics to study gene expression.

Main Results:

• Commensal bacteria trigger ROS production in an immune receptor- and RBOHD-dependent manner.
• RBOHD selectively inhibits specific commensals, including Xanthomonas L148.
• Mutation in L148's gspE gene, encoding a type II secretion system (T2SS) component, abrogates its detrimental effects on rbohD mutant plants.
• RBOHD suppresses bacterial T2SS gene expression, including gspE.
• Inhibition of gspE by ROS or mutation renders L148 protective against a bacterial pathogen.

Conclusions:

• A negative feedback loop exists between Arabidopsis ROS and bacterial T2SS.
• This loop tames potentially detrimental leaf commensals, converting them into beneficial microbes.
• RBOHD-mediated ROS production is crucial for maintaining a beneficial plant microbiota.