Nuclear importin α1 AtIMPA1 regulates stomatal reopening to defend against Pst DC3000 by orchestrating ABA signaling

Importin α family proteins serve as essential carriers for transporting specific disease-resistant proteins into the nucleus, enabling these proteins to function properly. However, whether importin α proteins are involved in plant immunity remains unclear. Here, we characterized a guard cell-expressed protein importin α1 AtIMPA1, which contributed to resistance against Pseudomonas syringae pv. tomato DC3000 (Pst DC3000). When dip-inoculated with Pst DC3000, the impa1 mutants exhibited increased susceptibility, along with significant stomatal reopening induced by the phytotoxin coronatine (COR) secreted by Pst DC3000; while overexpression of AtIMPA1 enhanced resistance to Pst DC3000 with compromised stomatal reopening induced by COR. Notably, following syringe-infiltration of Pst DC3000, the impa1 mutants showed increased resistance, whereas overexpression lines were more susceptible to Pst DC3000, indicating that COR-triggered stomatal reopening is a primary determinant in AtIMPA1-mediated disease resistance. Further investigations revealed that AtIMPA1 regulated COR-triggered stomatal reopening is linked to abscisic acid (ABA) signaling. Mutation of AtIMPA1 attenuated the ABA-mediated inhibition of root length and seed germination, and disrupted the ABA-induced protein abundance and localization of the ABA-responsive protein, supporting its role in regulating the ABA response. These findings shed light on the functional significance of AtIMPA1 in COR-triggered stomatal reopening and provided new insights into how importin α proteins orchestrate ABA signaling to regulate plant immunity.