Abstract
In oilseed plants, peroxisomal β-oxidation functions not only in lipid catabolism but also in jasmonate biosynthesis and metabolism of pro-auxins. Subfamily D ATP-binding cassette (ABC) transporters mediate import of β-oxidation substrates into the peroxisome, and the Arabidopsis ABCD protein, COMATOSE (CTS), is essential for this function. Here, the roles of peroxisomal ABCD transporters were investigated in barley, where the main storage compound is starch. Barley has two CTS homologues, designated HvABCD1 and HvABCD2, which are widely expressed and present in embryo and aleurone tissues during germination. Suppression of both genes in barley RNA interference (RNAi) lines indicated roles in metabolism of 2,4-dichlorophenoxybutyrate (2,4-DB) and indole butyric acid (IBA), jasmonate biosynthesis, and determination of grain size. Transformation of the Arabidopsis cts-1 null mutant with HvABCD1 and HvABCD2 confirmed these findings. HvABCD2 partially or completely complemented all tested phenotypes of cts-1. In contrast, HvABCD1 failed to complement the germination and establishment phenotypes of cts-1 but increased the sensitivity of hypocotyls to 100 μM IBA and partially complemented the seed size phenotype. HvABCD1 also partially complemented the yeast pxa1/pxa2Δ mutant for fatty acid β-oxidation. It is concluded that the core biochemical functions of peroxisomal ABC transporters are largely conserved between oilseeds and cereals but that their physiological roles and importance may differ.
Highlights
The peroxisome is the sole site of β-oxidation of fatty acids for very long chain fatty acid metabolism and signalling in and related molecules in plants and fungi, and is required mammals (Baker et al, 2006; Poirier et al, 2006; Wanders4834 | Mendiondo et al.and Waterham, 2006)
Comparative analysis of sequenced plant genomes has revealed that cereals contain two CTS homologues, consistent with a gene duplication occurring after divergence of the Suppression of HvABCD1 and HvABCD2 affects grain size but not germination
Abundance of HvABCD1 and HvABCD2 transcripts varied from 22% to 59% and 22% to 40% of levels measured in corresponding null segregant lines, respectively (Fig. 1B)
Summary
The peroxisome is the sole site of β-oxidation of fatty acids for very long chain fatty acid metabolism and signalling in and related molecules in plants and fungi, and is required mammals (Baker et al, 2006; Poirier et al, 2006; Wanders4834 | Mendiondo et al.and Waterham, 2006). Β-oxidation is important during germination, seedling establishment, fertilization, and dark-induced senescence, and in a number of additional key roles (reviewed in Theodoulou and Eastmond, 2012; Linka and Theodoulou, 2013). Acyl-activating enzymes re-esterify the fatty acids to CoA in the peroxisome lumen, which is a prerequisite for entry into β-oxidation (Fulda et al, 2004; De Marcos Lousa et al, 2013). This unusual transport mechanism appears to be common to plant, yeast, and mammalian ABCD proteins (van Roermund et al, 2012)
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