Nuclear events in ethylene signaling in Arabidopsis thaliana
The plant hormone ethylene participates in many developmental processes, yet the molecular mechanisms of its action are only beginning to be uncovered. In order to elucidate the signal transduction events that lead to changes in expression of ethylene-responsive genes, I cloned and characterized several AP2-domain-containing transcription factors. I focused on a small family of novel transcription factors, called Ethylene-Response DNA-Binding Factors (EDFs), that work immediately downstream of the transcriptional activator EIN3. All four members of this family show ethylene-inducible expression. Gel-shift assays and in planta GUS reporter studies demonstrate that the EIN3 protein binds to the promoter of the EDF1 gene, both in vitro and in vivo. The EDF proteins possess two DNA-binding domains, AP2 and B3-like, that in vitro recognize a bipartite DNA element, RBS. To address the in planta function of EDFs, gain- and loss-of-function strategies have been employed. Overexpression studies revealed that a truncated version of EDF1 can trigger constitutive activation and repression of different branches of the ethylene signaling pathway. Knockout mutant analysis suggested that the functions of the EDF genes are largely redundant. Weak ethylene insensitivity of the quadruple edf1 edf2 edf3 edf4 mutant implied the requirement of the EDF gene products for the normal responsiveness to this gas. Addition of the ctr1 mutation to the quadruple edf knockout revealed the ability of the quad to partially suppress constitutive ethylene signaling initiated by ctr1. ^ Microarray technology has been utilized to examine molecular changes induced in plants after exogenous application of ethylene. Gene expression analysis revealed that many aspects of plant growth and metabolism were affected by the gas. Mutations in the edf genes and EDF1/ EDF2 overexpression resulted in abnormal expression of a subclass of ethylene-regulated genes. Several genes that possess an RBS in their promoters and show altered expression levels in the mutants represent potential in vivo targets of the EDF proteins. ^ Two other complementary approaches, transposon mutagenesis and yeast two-hybrid, have been employed to identify novel components of the ethylene signaling pathway. Genetic and phenotypic analysis of the resulting mutants and preliminary characterization of EIL1- and EIL2-interacting clones are presented. ^
Biology, Molecular|Biology, Genetics|Biology, Plant Physiology
Anna Nickolaevna Stepanova,
"Nuclear events in ethylene signaling in Arabidopsis thaliana"
(January 1, 2001).
Dissertations available from ProQuest.