ASYMMETRIC LEAVES1 is phosphorylated by MPK3/6 in Arabidopsis thaliana

Abstract

Mitogen-activated protein kinases (MPKs) play a crucial role in the regulation of many aspects of plant growth, development, and responses to the environment. In Arabidopsis, MPK3 and MPK6 are known to be implicated in embryonic and stomatal development as well as biotic and abiotic stress responses. However, the regulation mechanisms of plant developments by MPKs are poorly understood. Here, we provide direct evidences that ASYMMETRIC LEAVES1 (AS1), a MYB transcription factor, is phosphorylated by AtMPK3 and AtMPK6. We also show the direct interactions between AS1 and AtMPK3/6 by using yeast and plant systems. In addition, we identified the phosphorylation of AS1 by recombinant AtMPK3 and AtMPK6 by in vitro kinase assays. Using site-directed mutagenesis assay, we identified that the 202(th) serine residue of AS1 was specifically phosphoylated by MPK3/6. Finally, we confirmed that AS1 could be phosphorylated by endogenous AtMPK3/6 using in-gel kinase assays. These results suggest that the phosphorylation of AS1 by MPKs may be one of regulation modes for leaf development in plants.