Genetic and molecular characterization of REVERSION -TO-ETHYLENE –SENSITIVITY-1 (RTE1).
Ethylene is a gaseous plant hormone that has profound effects on plant growth and development. Genetic analysis has been central in the elucidation of the ethylene-signaling pathway, made possible through screens for both insensitive and constitutive response mutants. Ethylene-insensitive mutants fail to exhibit the classic triple response displayed by Arabidopsis seedlings grown in the dark in the presence of ethylene. The etr1-2 mutant receptor confers weak ethylene insensitivity, and unlike other insensitive alleles can still bind ethylene. We utilized etr1-2 in a screen for new components in the ethylene-signaling pathway, and identified the REVERSION-TO-ETHYLENE –SENSITIVITY-1 (RTE1) locus. Loss of RTE1 function results in suppression of the etr1-2 insensitive phenotype, but is unable to suppress the insensitivity of stronger dominant insensitive mutants. Single mutant analysis revealed a phenotype reminiscent of ETR1 loss of function mutants, and further analysis of double mutants suggests that loss of RTE1 results in a non-functional ETR1. RTE1 was found to encode a novel integral membrane protein with homologues in other plants and also animals. RTE1 has a single homologue in Arabidopsis, which we have named RTE2, and which we speculate may have a redundant function. Sequence analysis reveals two regions of conserved cysteine and histidine residues, which are common in metal binding proteins; one allele of RTE1 encodes a missense mutation at one of these cysteine residues. One hypothesis is that RTE1 may be important in binding metal ions, more specifically that it may be involved in the binding or association of the copper cofactor which is essential for ethylene binding.
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