Actin depolymerization factor (ADF) moonlighting: Nuclear immune regulation by interacting with WRKY transcription factors and shaping the transcriptome.

Abstract

Remodeling of the actin cytoskeleton is a critical process for plant immunity, essential for the transport, activation, and stabilization of immune-regulatory molecules and organelles. In this process, actin depolymerization factors (ADFs) function as key players through severing and depolymerizing actin microfilaments. However, recent evidence suggests that ADFs may possess noncanonical immune functions inside the nucleus, in addition to the canonical cytosolic role, a phenomenon not adequately explained by the traditional mechanistic model of ADF-actin dynamics. In this study, we demonstrate that Arabidopsis ADFs exhibit a moonlighting function in the nucleus, where they interact with transcriptional machinery to regulate the transcriptome during both the resting state and the immune responses. We show that ADF2/3/4 have redundant functions in defense against virulent and avirulent Pseudomonas syringae. Notably, it is nuclear-rather than cytosolic-ADFs that majorly contribute to defense against P. syringae and mediate proimmune transcription. Mechanistically, we demonstrate that nuclear ADFs interact with transcription factors, histone complexes, and other components of the transcriptional machinery. Specifically, ADF2/3/4 can form a complex with WRKY transcription factors, such as WRKY22/29/48, thereby directly regulating WRKY activity to shape the proimmune transcriptome. In summary, our study reveals that ADFs moonlight as direct regulators of transcription factors, mediating a broad range of nuclear-cytoplasmic regulation in plant immunity and potentially other biological processes.