Phosphorylation-dependent differential regulation of plant growth,cell death,and innate immunity by the regulatory receptor-like kinase BAK1

Plants rely heavily on receptor-like kinases (rlks) for perception and integration of external and internal stimuli. the arabidopsis regulatory leucine-rich repeat rlk (lrr-rlk) bak1 is involved in steroid hormone responses,innate immunity,and cell death control. here,we describe the differential regulation of three different bak1-dependent signaling pathways by a novel allele of bak1,bak1-5. innate immune signaling mediated by the bak1-dependent rks fls2 and efr is severely compromised in bak1-5 mutant plants. however,bak1-5 mutants are not impaired in br signaling or cell death control. we also show that,in contrast to the rd kinase bri1,the non-rd kinases fls2 and efr have very low kinase activity,and we show that neither was able to trans-phosphorylate bak1 in vitro. furthermore,kinase activity for all partners is completely dispensable for the ligand-induced heteromerization of fls2 or efr with bak1 in planta,revealing another pathway specific mechanistic difference. the specific suppression of fls2- and efr-dependent signaling in bak1-5 is not due to a differential interaction of bak1-5 with the respective ligand-binding rk but requires bak1-5 kinase activity. overall our results demonstrate a phosphorylation-dependent differential control of plant growth,innate immunity,and cell death by the regulatory rlk bak1,which may reveal key differences in the molecular mechanisms underlying the regulation of ligand-binding rd and non-rd rks. © 2011 schwessinger et al.