Phosphorylation by AtMPK6 is required for the biological function of AtMYB41 in Arabidopsis

Mitogen-activated protein kinases (MPKs) are involved in a number of signaling pathways that control plant development and stress tolerance via the phosphorylation of target molecules. However, so far only a limited number of target molecules have been identified. Here, we provide evidence that MYB41 represents a new target of MPK6. MYB41 interacts with MPK6 not only in vitro but also in planta. MYB41 was phosphorylated by recombinant MPK6 as well as by plant MPK6. Ser(251) in MYB41 was identified as the site phosphorylated by MPK6. The phosphorylation of MYB41 by MPK6 enhanced its DNA binding to the promoter of a LTP gene. Interestingly, transgenic plants over-expressing MYB41(WT) showed enhanced salt tolerance, whereas transgenic plants over-expressing MYB41(S251A) showed decreased salt tolerance during seed germination and initial root growth. These results indicate that the phosphorylation of MYB41 by MPK6 is required for the biological function of MYB41 in salt tolerance.