H2S-modulated alternative splicing of the protein phosphatase gene <i>HAB2</i> drives divergent stomatal dynamics in Arabidopsis

Abscisic acid (ABA) serves as a critical regulator of plant adaptive responses to environmental stresses. Currently, the function of HOMOLOGY TO ABI2 (HAB2) of Arabidopsis, a member of the ABA signaling component the protein phosphatase 2C family (PP2C), remains uncharacterized. Hydrogen sulfide (H2S) plays a vital role throughout the plant life cycle. We found that exogenous H2S induced stomatal closure in Arabidopsis hab2 mutants. Detailed characterization then showed that HAB2 underwent alternative splicing (AS), generating three transcripts that we designated as HAB2.1-2.3, with HAB2.2 targeted for degradation. H2S affected the AS of HAB2 through RNA recognition motif (RRM)-containing protein 25 (RBM25), with HAB2.1 and HAB2.3 playing distinct roles in H2S-regulated stomatal movement. HAB2.1 interacted with PYL3 and PYL5-13, whereas HAB2.3 lost this interaction. Additionally, both HAB2.1 and HAB2.3 physically interacted with SnRK2s, but their effects on inhibiting OPEN STOMATA1 (OST1) phosphorylation differed significantly. Finally, we found that HAB2.1 and HAB2.3 had opposite functions in ABA sensitivity, stomatal movement, and drought tolerance. Overall, our results show that H2S regulates the AS pattern of HAB2 through RBM25, thereby promoting stomatal closure, and in this regard, HAB2.1 and HAB2.3 play significantly different roles. Our study not only indicates a new potential mechanism by which H2S regulates stomatal movement by altering the AS pattern, but also reveals the functional differences between HAB2.1 and HAB2.3 in Arabidopsis.