Abstract
Rice WRKY45 is a key transcription factor that mediates salicylic acid (SA) defense signaling pathway, and protein phosphorylation is possibly involved in its regulation. Our previous results showed that OsMPK6 was specifically activated by SA in rice cultured cells. However, since OsMPK6 has been implicated in various signaling pathways, its upstream kinases (MAPKKs) presumably play a key role in determining the pathway specificity of MAP kinase cascades. To investigate an SA-pathway-specific MAP kinase cascade leading to WRKY45 activation, we have functionally characterized rice MAPKKs.
In vitro phosphorylation assays using 4 recombinant MAPKK proteins expressed in E. coli showed that OsMPK6 was most strongly phosphorylated by OsMKK10-2. A GST-pulldown assay revealed that OsMKK10-2 strongly binds to OsMPK6. We also showed that dexamethazone-induced expression of OsMKK10-2 proteins resulted in the phosphorylation/activation of OsMPK6 and the upregulation of WRKY45 transcript levels in transgenic rice cells. We will also discuss the signaling specificity of OsMKK10-2-OsMPK6 cascade and its role in disease resistance.
