From Endoplasmic Reticulum （ER） to Nucleus： EIN2 Bridges the Gap in Ethylene Signaling
摘要
The phytohormone ethylene plays essential roles in regulating plant growth and development.Understanding the mechanism of ethylene biosynthesis,signal transduction,and downstream responses is of great importance to frame the entire processes of plant growth.Genetic and biochemical approaches were applied in recent years to help establish an approximately linear ethylene signaling pathway.Ethylene gas molecules are perceived by a five-member endoplasmicreticulum (ER)-Iocalized receptor family,including ETR1,ETR2,ERS1,ERS2,and EIN4.In the presence of ethylene,the receptors relieve the suppression of downstream responses by deactivating negative regulator CTR1,a Raf-like protein kinase (Kieber et al.,1993),whose function as a MAPKKK in ethylene signaling is still under debate (Zhao and Guo,2011).Downstream of CTR1,the signal is transmitted via an essential positive regulator EIN2,and subsequently to transcription factors EIN3/EIL1 by protecting them from EBF1/2-mediated ubiquitin-proteasome degradation,thus reprogramming the transcriptional cascade in the nucleus (Zhao and Guo,2011).