FIMBRIN2 Regulates ABA‐Induced Stomatal Closure by Promoting Microfilament Bundling and Turnover in Arabidopsis Guard Cells

ABSTRACT In terrestrial plants, drought stress activates abscisic acid (ABA) signaling in guard cells, prompting stomatal closure to reduce water loss. Stomatal closure is accompanied by reorganization of the microfilaments. However, the mechanism by which ABA signaling regulates microfilaments disassembly remains unclear, and the actin‐binding proteins (ABPs) involved in this process have yet to be fully identified. In this study, we demonstrated that FIMBRIN2 (FIM2), an actin‐bundling protein, has its expression in guard cells upregulated by ABA, and FIM2 is involved in ABA‐induced stomatal closure. The fim2 mutant exhibits a drought‐sensitive phenotype and delayed stomatal closure. Further confocal microscopy observations confirmed that this delay results from impaired actin bundling and reduced actin turnover activity. These findings reveal FIM2's role in ABA‐induced stomatal closure and deepen our understanding of the functions of ABPs and the actin cytoskeleton in plant stress adaptation.