Phosphorylation of the zinc finger transcriptional regulator ZAT6 by MPK6 regulates Arabidopsis seed germination under salt and osmotic stress.

C(2)H(2)-type zinc finger proteins (ZFPs) play diverse roles in plant response to abiotic stresses. ZAT6, an Arabidopsis C(2)H(2)-type ZFP, has been reported to regulate root development and nutrient stress responses. However, its roles in regulation of abiotic stress response are incompletely known. Here, we demonstrate that salt or osmotic stress triggers a strong increase in ZAT6 expression in leaves. Transgenic plants overexpressing ZAT6 showed improved seed germination under salt and osmotic stress. Intriguingly, ZAT6 interacts with a stress-responsive mitogen-activated protein kinase MPK6 in vitro and in planta. ZAT6 is phosphorylated by both recombinant and plant endogenous MPK6. Serine 8 and serine 223 in ZAT6 were identified as the sites phosphorylated by MPK6. In contrast to wild-type form of ZAT6, overexpression of phosphorylation mutant form did not display significantly enhanced salt and osmotic stress tolerance. Altogether, our results suggest that phosphorylation by MPK6 is required for the functional role of ZAT6 in seed germination under salt and osmotic stress.