Abstract
Innate immunity signaling pathways in plants are regulated by mitogen-activated protein kinase (MAPK) cascades. Arabidopsis MEKK1, a MAPK kinase kinase (MAPKKK) is an important factor of innate immunity signaling in the upstream of MPK4 which has at least two functions, negative regulation of defense-related responses and positive regulation of camalexin biosynthesis upon pathogen challenge. MEKK1 is essential for flg22- and H2O2-induced MPK4 activation, however regulatory mechanism of MEKK1 remains to be elucidated.
To identify possible regulator of MEKK1, we performed yeast two-hybrid screening using MEKK1 protein as bait. We found two MEKK1-binding proteins which contain U-box domain. Protein harboring this domain is thought to be function as an ubiquitin E3 ligase. In vitro ubiquitylation assay suggests that these proteins are functional E3 lingases. These results suggest presence of ubiquitin-mediated regulation of MEKK1.
