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

Abstract

Indole-3-butyric acid (IBA) and 2,4-dichlorophenoxybutyric acid (2,4-DB) are metabolised by peroxisomal beta-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 beta-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.

Multiple Facets ofArabidopsisSeedling Development Require 
Indole-3-Butyric Acid–Derived Auxin

“…Bar = 1 cm. characterized (Zolman et al, 2007(Zolman et al, , 2008Wiszniewski et al, 2009). By contrast, no T-DNA insertions have been reported in IBR10 or ECH2, and only single alleles have emerged from IBA response screens: ibr10-1, which results in a 26-amino acid inframe deletion (Zolman et al, 2008), and ech2-1, a missense allele (Figure 1), consistent with the possibility that null alleles of ibr10 and ech2 may confer more severe defects than the alleles that have been recovered to date.…”

Plant Peroxisomes: Biogenesis and Function

“…In addition to hydratase activity, ECH2 also has a hot dog domain common in thioesterases and therefore may be acting at the last step to convert IAACoA to IAA . Finally, IBR1, also identified as SDRa (Wiszniewski et al, 2009), encodes a short-chain dehydrogenase/reductase (Zolman et al, 2008), which may catalyze the fourth step of IBA b-oxidation. AIM1-IBR1 redundancy at the dehydrogenase/reductase step could explain why the ibr1 defects are less severe than those of other mutants .…”

“…Furthermore, two steps remain unresolved. The aae18 synthetase mutant is 2,4-DB resistant but responds normally to IBA (Wiszniewski et al, 2009); whether a different protein activates IBA (perhaps redundantly) remains to be determined. IAA export to the cytosol has not been defined either.…”

“…The physiological functions of a number of enzymes and metabolic pathways indicated by proteomic data have been verified. Examples include the oxidative pentose phosphate pathway (Meyer et al, 2011), betaine aldehyde dehydrogenase (Missihoun et al, 2011), SDRa (Wiszniewski et al, 2009), and the bifunctional transthyretin-like protein involved in purine catabolism and S-allantoin biosynthesis (Lamberto et al, 2010), which have significantly broadened our knowledge of peroxisome metabolism.…”

Peroxisomal ATP-Binding Cassette Transporter COMATOSE and the Multifunctional Protein ABNORMAL INFLORESCENCE MERISTEM Are Required for the Production of Benzoylated Metabolites in Arabidopsis Seeds

“…S1; Supplemental Table S1) was analyzed for glucosinolates, including BGs (Reichelt et al, 2002), and phenolic choline esters such as hydroxycinnamoylcholine and hydroxybenzoylcholine esters (Böttcher et al, 2009). Most of these mutants were analyzed previously for potential roles in fatty acid or auxin metabolism, but the specific functions of the genes involved remain unknown (Wiszniewski et al, 2009). Since glucosinolate profiles vary significantly among different Arabidopsis ecotypes (Kliebenstein et al, 2001(Kliebenstein et al, , 2007, we analyzed mutants from a single ecotype background, Columbia (Col-0), to permit ready comparison among mutant lines.…”