PSRP2 interacts with F-box protein FOF2 to regulate ABA and drought response in Arabidopsis

The phytohormone abscisic acid (ABA) plays a central role in regulating key plant processes, including seed germination and drought adaptation. Although our previous work implicated F-box of flowering 2 (FOF2) in ABA-mediated germination and drought responses, its molecular mechanism remained unclear. Here, we demonstrate that plastid-specific ribosomal protein 2 (PSRP2) physically interacts with FOF2 both in vitro and in vivo. Expression of PSRP2 is suppressed under ABA treatment and drought stress. Phenotypically, the psrp2 mutant exhibits reduced sensitivity to ABA during seed germination and early seedling growth, whereas PSRP2-overexpressing plants are hypersensitive. Interestingly, in contrast to its role in germination, loss of PSRP2 enhances ABA sensitivity in stomatal regulation, leading to more efficient stomatal closure, reduced water loss, and improved drought tolerance. RNA-seq analysis indicated that drought stress modulates the expression of drought- and ABA-responsive genes in the psrp2 mutant. Genetic analysis revealed that the fof2 mutation largely suppresses the psrp2 mutant phenotype in response to ABA and drought. Collectively, our results identify a PSRP2-FOF2 module that promotes ABA-mediated seed germination and seedling establishment, while negatively regulating ABA-dependent stomatal responses and drought tolerance.