Elucidating genetic mechanisms of plant host immune suppression by commensal bacteria using RB-TnSeq mutant libraries

Abstract

Plant-microbe interactions have an important role in determining plant phenotype and fitness. One key form of interaction is mediated through the innate plant immune system, which functions to fight off pathogens by identifying non-self molecules known as microbe associated molecular patterns (MAMPs). Beneficial and commensal microbes also possess these MAMPs. Increasing evidence shows that non-pathogenic microbes are able to overcome the plant immune system in order to successfully colonize plants, but the underlying mechanisms remain to be fully understood. Random barcoded transposon-site sequencing (RB-TnSeq) has emerged as a technique to create large mutant libraries that help elucidate gene mechanisms in bacteria. This study established RB-TnSeq mutant libraries of two commensal bacterial strains, Variovorax paradoxus CL14 and Brevundimonas sp. MF374. The MF374 mutant library was screened for loss of immune suppression in Arabidopsis seedlings and a peptidyl-prolyl cis-trans isomerase D gene was identified as a potential gene conferring the ability of plant immune suppression. These results provide a potential genetic mechanism for plant immune suppression by Brevundimonas MF374. Future work should be focused on validating the peptidyl-prolyl cis-trans isomerase D mutant and screening the RB-TnSeq mutant libraries to further understand the mechanisms underlying plant-microbe interactions.