avrEDspE

AvrEDspE is a type III secretion system effector protein identified in the phytopathogenic bacterium Xanthomonas campestris pv. campestris. The gene encoding this effector, which was initially named avrEDspE due to its predicted avirulence function in Arabidopsis, was cloned during genome sequencing efforts that sought to catalog the full complement of secreted proteins contributing to host interaction. Bioinformatic analysis places AvrEDspE within a family of N-terminally secretory proteins that share a conserved predicted translocation signal but lack a recognizable catalytic domain, suggesting a protein–protein interaction role within the host cytoplasm.

Functional studies demonstrate that AvrEDspE suppresses hypersensitive response (HR) in susceptible Brassica hosts while eliciting HR in resistant lines that possess a corresponding resistance gene, REDspE. The effector appears to target host defense signaling pathways, possibly interfering with the function of upstream mitogen-activated protein kinases. Mutants lacking avrEDspE exhibit attenuated virulence on Brassica rapa but can still cause disease on more permissive hosts, indicating a species-specific interaction. Transgenic Arabidopsis overexpressing avrEDspE shows enhanced susceptibility to bacterial invasion and reduced expression of pathogenesis-related genes.

Research on AvrEDspE has implications for the development of durable disease resistance. By characterizing the effector’s molecular targets, breeding programs can identify R genes that recognize AvrEDspE, leading to crops capable of recognizing and responding to this virulence factor. The ongoing investigation of AvrEDspE and its host interactions remains a model for understanding effector biology in bacterial plant pathogens.