Abstract
Mitogen-activated protein kinase (MAPK) cascades are universal signal transduction modules in eukaryotes. In plants, MAPK cascades are known to function in various biotic and abiotic stress signaling. Completion of the Arabidopsis genome-sequencing project has revealed the existence of 20 MAPKs, 10 MAPK kinases and 60 MAPK kinase kinases. Here we studied AtMKK3, one of the Arabidopsis MAPK kinases, and analyzed which AtMPKs were substrates for AtMKK3 by in vitro activation assay. In this assay, we found that AtMKK3 specifically activate AtMPK6 and AtMPK8. Then, we used the transgenic Arabidopsis plants that express the AtMKK3 under the control of a steroid-inducible promoter. Induction of the dexamethasone dependent AtMKK3 expression activated the endogenous AtMPK6 as revealed by the analysis using in-gel kinase assay coupled with immunoprecipitation with Ab6NT1. These results indicated that functional interaction between AtMKK3 and AtMPK6 in vivo. We will discuss the physiological role of the AtMKK3-AtMPK6 pathway.
