Xanthomonas Type III Effector XopN Targets Scaffold Protein OsRACK1B to Suppress Rice Immunity.

Area of Science:

• Plant Pathology
• Molecular Plant-Microbe Interactions
• Rice Immunity

Background:

• Bacterial leaf streak (BLS), caused by Xanthomonas oryzae pv. oryzicola (Xoc), significantly threatens global rice production.
• Understanding how Xoc effectors manipulate plant immune signaling is crucial for developing disease resistance strategies.

Purpose of the Study:

• To elucidate the molecular mechanisms by which the Xoc effector XopN suppresses rice basal immunity.
• To identify and characterize the host targets of XopN involved in rice immune signaling.

Main Methods:

• Yeast two-hybrid screening to identify XopN interacting partners.
• Bimolecular fluorescence complementation and pull-down assays to confirm protein interactions.
• Functional analysis of OsRACK1B in rice, including overexpression and loss-of-function mutants.

Main Results:

• The Xoc effector XopN directly targets the rice WD40-repeat protein OsRACK1B.
• OsRACK1B positively regulates rice basal immunity; its overexpression enhances resistance, while loss-of-function mutants are more susceptible.
• OsRACK1B interacts with the transcription factor OsRap2.6, forming an immune module disrupted by XopN.

Conclusions:

• XopN suppresses rice basal immunity by competitively binding to OsRACK1B, thereby inhibiting the OsRACK1B-OsRap2.6 immune complex.
• This study reveals a novel virulence strategy employed by Xoc to subvert host defenses through targeting scaffold protein complexes.
• Findings provide critical insights into the molecular basis of Xoc pathogenicity and rice innate immunity.