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

SUMMARY

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.