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MAP4K1 and MAP4K2 regulate ABA-induced and Ca2+-mediated stomatal closure in Arabidopsis

Yamashita, K.; Katagiri, S.; Takase, H.; Li, Y.; Otoguro, A.; Kamiyama, Y.; Yamauchi, S.; Takemiya, A.; Mori, I. C.; Umezawa, T.

2024-07-05 plant biology
10.1101/2024.07.05.602132 bioRxiv
Show abstract

Abscisic acid (ABA)-induced stomatal closure limits water loss from plants under drought stress. To investigate signaling pathways involved in stomatal closure, we performed a phosphoproteomic analysis of ABA-treated Arabidopsis guard cell protoplasts (GCPs). From this analysis, we discovered that MITOGEN-ACTIVATED PROTEIN 4 KINASE 1 (MAP4K1) is phosphorylated in response to ABA. Subsequent biochemical assays showed that Ser-479 of MAP4K1 is directly phosphorylated by SRK2E (OST1/SnRK2.6), a protein kinase that plays a central role in ABA-induced responses. Mutational analyses of MAP4K1, as well as closely related MAP4K2, revealed that both kinases positively regulate ABA-induced stomatal closure, and that Ser-479 of MAP4K1 was required for this phenotype. In map4k1map4k2, stomatal closure was induced by exogenous Ca2+ but not H2O2. Furthermore, electrophysiology experiments showed that MAP4K1/2 are required for ABA-dependent activation of Ca2+-permeable channels in GCPs. Together, our results indicate that SnRK2 and MAP4K1/2 function as a signaling module to regulate Ca2+-mediated stomatal closure.

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