Nuclear ubiquitin proteasome degradation affects WRKY45 function in the rice defense program

Area of Science:

• Plant molecular biology
• Plant immunity
• Post-translational regulation

Background:

• WRKY45 is a key transcriptional activator in rice's salicylic acid-induced defense.
• The ubiquitin-proteasome system (UPS) is a major cellular protein degradation pathway.

Purpose of the Study:

• To investigate the role of the nuclear UPS in regulating WRKY45 function in rice.
• To compare UPS-mediated regulation of salicylic acid pathway components between rice and Arabidopsis.

Main Methods:

• Treatment of rice cells with proteasome inhibitors.
• Analysis of WRKY45 ubiquitination and gene expression.
• Site-directed mutagenesis of WRKY45, including its nuclear localization signal and C-terminal region.
• Comparison with Arabidopsis NPR1 regulation.

Main Results:

• The nuclear UPS mediates the degradation of WRKY45 in rice.
• UPS-dependent degradation of WRKY45 occurs in the nucleus and suppresses defense gene expression.
• Proteasome inhibition impairs WRKY45's transcriptional activity, with the C-terminal region being crucial for both activity and degradation.
• Unlike Arabidopsis NPR1, rice OsNPR1/NH1 is not stabilized by proteasome inhibition under uninfected conditions.

Conclusions:

• Nuclear UPS regulation is critical for controlling WRKY45 activity and rice defense.
• Post-translational regulation of salicylic acid pathway components differs between rice and Arabidopsis.