Identification of two Arabidopsis genes encoding a peroxisomal oxidoreductase-like protein and an acyl-CoA synthetase-like protein that are required for responses to pro-auxins
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Indole-3-butyric acid (IBA) and 2,4-dichlorophenoxybutyric acid (2,4-DB) are metabolised by peroxisomal β-oxidation to active auxins that inhibit root growth. We screened Arabidopsis mutants for resistance to IBA and 2,4-DB and identified two new 2,4-DB resistant mutants. The mutant genes encode a putative oxidoreductase (SDRa) and a putative acyl-activating enzyme (AAE18). Both proteins are localised to peroxisomes. SDRa is coexpressed with core β-oxidation genes, but germination, seedling growth and the fatty acid profile of sdra seedlings are indistinguishable from wild type. The sdra mutant is also resistant to IBA, but aae18 is not. AAE18 is the first example of a gene required for response to 2,4-DB but not IBA. The closest relative of AAE18 is AAE17. AAE17 is predicted to be peroxisomal, but an aae17 aae18 double mutant responded similarly to aae18 for all assays. We propose that AAE18 is capable of activating 2,4-DB but IBA activating enzymes remain to be discovered. We present an updated model for peroxisomal pro-auxin metabolism in Arabidopsis that includes SDRa and AAE18.
KeywordsAcyl-activating enzyme Auxin Indole-3-butyric acid Peroxisome β-Oxidation
This project was funded by the Australian Research Council (Grants FF0457721 and CE0561495), the Western Australian Government’s Centre of Excellence Program and an Australian Postgraduate Award to AAGW. We thank Peter Eastmond for kind donation of sucrose dependent lines from which we obtained kat2-2. We thank also ABRC, SALK, INRA Versailles, NASC, GABI and CSHL for T-DNA seed lines.
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