Bacterial host adaptation through sequence and structural variations of a single type III effector gene

Area of Science:

• Plant-pathogen interactions
• Molecular plant pathology
• Bacterial effector function

Background:

• Quantitative variations in pathogen virulence are not well understood.
• Plant immune receptors often recognize conserved effector domains.
• Effector evolution can drive host adaptation.

Purpose of the Study:

• To investigate the molecular mechanisms of Xanthomonas campestris XopJ6 effector function.
• To understand how XopJ6 contributes to bacterial pathogenicity and host adaptation.
• To explore the role of genetic variation in XopJ6 in plant immune evasion.

Main Methods:

• Identification and characterization of the XopJ6 effector from Xanthomonas campestris.
• Analysis of XopJ6 interaction with plant immune receptors (RRS1-R/RPS4 NLR pair).
• Investigation of XopJ6 natural variants and their impact on effector function and immune recognition.
• Utilizing synthetic biology to study the effect of xopJ6 copy number variation (CNV) on virulence.

Main Results:

• XopJ6 triggers disease resistance in Arabidopsis thaliana and cauliflower.
• A natural XopJ6 variant with a mutation in the WRKY-binding site evades immune detection while retaining virulence.
• The xopJ6 gene is located on a transposon, facilitating copy number variation (CNV).
• xopJ6 CNV modulates Xanthomonas campestris virulence on Arabidopsis through gene dosage effects.

Conclusions:

• Sequence and structural variations in effector genes, like XopJ6, are key drivers of bacterial host adaptation.
• XopJ6's interaction with plant immune receptors and its variable copy number contribute to pathogen evolution.
• Understanding effector variation provides insights into molecular mechanisms of quantitative pathogenicity.