ETHYLENE SIGNALING IN ARABIDOPSIS - EVENTS FROM THE MEMBRANE TO THE NUCLEUS

Ethylene is a plant hormone that regulates a diverse set of developmen tal and physiological processes including seed germination, abscission , and senescence. Molecular genetic analysis of ethylene signaling in Arabidopsis thaliana, has led to the identification of a number of gen etic loci that are required for normal ethylene responses. Cloning of several of the mutant loci has provided significant insight into the n ature of the ethylene signaling pathway. The Raf kinase homolog CTR1 i s predicted to negatively regulate the ethylene response pathway throu gh a MAP kinase cascade. ETR1 has been demonstrated to bind ethylene, and a family of homologous genes encode products that may function in a receptor complex. EIN3 and three homologous gene products contain se veral protein motifs that are reminiscent of transcription factors, an d transduce the ethylene signal downstream. Additional loci are define d by the ein2, ein5/ain1, ein6, and ein7 mutations, and a number of mu tations defining tissue-specific mediators of ethylene responses have also been identified. In this review, the different ethylene-related m utations and their gene products are considered in detail, and possibl e models of the manner in which the pathway functions are proposed. (C ) Elsevier, Paris.