Xanthomonas coordinates type III-type II effector synergy by activating fruit-ripening pathway

Area of Science:

• Plant Pathology
• Microbial Pathogenesis
• Molecular Plant-Microbe Interactions

Background:

• Plant cell walls contain abundant carbohydrates, but the mechanisms pathogens use to access these reserves are not fully understood.
• The citrus canker pathogen, Xanthomonas citri subsp. citri (Xcc), is a significant agricultural threat.

Purpose of the Study:

• To elucidate the molecular mechanisms by which Xcc mobilizes plant cell wall carbohydrates.
• To investigate the role of the type III effector PthA4 in Xcc pathogenesis and nutrient acquisition.

Main Methods:

• Utilized transcriptomics and reporter assays to analyze gene expression changes in host plants and bacteria.
• Investigated the function of the type III effector PthA4 and its interaction with host factors like CsLOB1.
• Examined the activation of the Xcc xylan CUT system and its components, including xylanase.

Main Results:

• The type III effector PthA4 activates the host ripening coordinator CsLOB1, inducing genes for cell wall breakdown.
• CsLOB1 promotes Xcc growth even in non-fruiting plants, indicating a conserved mechanism.
• Host-derived xylose triggers the Xcc xylan CUT system, involving a type II-secreted xylanase.

Conclusions:

• Xcc employs a feedforward loop where PthA4-driven cell wall remodeling activates bacterial xylan utilization.
• This effector-driven strategy facilitates nutrient acquisition and fuels Xcc proliferation during infection.