Ethylene is a simple two-carbon gas that functions as a plant hormone. Ethylene is important at many stages of the plant's life, including seed germination, seedling growth, leaf and petal abscission, organ senescence, and pathogen responses.
Components of the ethylene signal transduction pathway have been identified by a mutational approach with Arabidopsis. The initial steps in ethylene signal transduction are shared for all these responses. Cloning of these genes has started to reveal how ethylene is perceived in plants. ETR1 (along with ERS1, ETR2, ERS2, and EIN4) are all related to the two-component signaling proteins from bacteria. CTR1 is related to the Raf-like serine/threonine protein kinases from mammals. EIN2 is related to the Nramp family of metal transporters. EIN3, EIL1, EIL2, and ERF1 are transcription factors.
ETR1 functions as an ethylene receptor. The aminoterminal region contains 3 transmembrane domains and the site of ethylene binding. The carboxyterminal half of the protein contains histidine kinase and response regulator domains. We have demonstrated histidine kinase activity in the ETR1 protein. We hypothesize that ETR1 could function analogously to the bacterial sensor proteins, with ethylene binding regulating activity of the histidine kinase domain. This may regulate some aspects of ethylene signaling.
The greatest level of amino acid identity between ETR1 and other members of this family is in the transmembrane domains; this is the region implicated in ethylene binding. There are some significant differences between ETR1 and other members of this family. Some members have response regulator domains while others do not. Some members have three transmembrane domains, while others have four. Some members have highly conserved histidine kinase domains, while other members show significant divergence and lack residues considered essential for activity. How these isoforms function in ethylene signaling is being studied using a combination of biochemical, molecular, and genetic techniques.
The information presented here
represents the efforts of several labs that investigate ethylene signal
transduction in Arabidopsis. Our interest is in the function of the
histidine kinase domain. Listed below some of the other labs and their
areas of interest.
Tony
Bleecker: Ethylene binding site of receptors.
Caren
Chang:
Proteins interacting with ethylene receptors
Joe
Ecker:Analysis
of ethylene signal transduction pathway
Joe
Kieber:
Control of ethylene synthesis and role of CTR1 in ethylene
signaling
Elliot
Meyerowitz:
Analysis of ethylene receptor family
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