ACTIVATION OF THE ETHYLENE GAS RESPONSE PATHWAY IN ARABIDOPSIS BY THENUCLEAR-PROTEIN ETHYLENE-INSENSITIVE3 AND RELATED PROTEINS

Mutations in the Arabidopsis ETHYLENE-INSENSITIVE3 (EIN3) gene severel y limit a plant's response to the gaseous hormone ethylene. ein3 mutan ts show a loss of ethylene-mediated effects including gene expression, the triple response, cell growth inhibition, and accelerated senescen ce. EIN3 acts downstream of the histidine kinase ethylene receptor, ET R1, and the Raf-like kinase, CTR1. The EIN3 gene encodes a novel nucle ar-localized protein that shares sequence similarity, structural featu res, and genetic function with three EIN3-LIKE (EIL) proteins. In addi tion to EIN3, EIL1 or EIL2 were able to complement ein3, suggesting th eir participation in the ethylene signaling pathway. Overexpression of EIN3 or EIL2 in wild-type or ethylene-insensitive2 plants conferred c onstitutive ethylene phenotypes, indicating their sufficiency for acti vation of the pathway in the absence of ethylene.