The Arabidopsis pxa1 Mutant Is Defective in an ATP-Binding Cassette Transporter-Like Protein Required for Peroxisomal Fatty Acid β-Oxidation

Abstract

Peroxisomes are important organelles in plant metabolism, containing all the enzymes required for fatty acid ␤-oxidation. More than 20 proteins are required for peroxisomal biogenesis and maintenance. The Arabidopsis pxa1 mutant, originally isolated because it is resistant to the auxin indole-3-butyric acid (IBA), developmentally arrests when germinated without supplemental sucrose, suggesting defects in fatty acid ␤-oxidation. Because IBA is converted to the more abundant auxin, indole-3-acetic acid (IAA), in a mechanism that parallels ␤-oxidation, the mutant is likely to be IBA resistant because it cannot convert IBA to IAA. Adult pxa1 plants grow slowly compared with wild type, with smaller rosettes, fewer leaves, and shorter inflorescence stems, indicating that PXA1 is important throughout development. We identified the molecular defect in pxa1 using a map-based positional approach. PXA1 encodes a predicted peroxisomal ATP-binding cassette transporter that is 42% identical to the human adrenoleukodystrophy (ALD) protein, which is defective in patients with the demyelinating disorder X-linked ALD. Homology to ALD protein and other human and yeast peroxisomal transporters suggests that PXA1 imports coenzyme A esters of fatty acids and IBA into the peroxisome for ␤-oxidation. The pxa1 mutant makes fewer lateral roots than wild type, both in response to IBA and without exogenous hormones, suggesting that the IAA derived from IBA during seedling development promotes lateral root formation.Peroxisomes are small, ubiquitous organelles encased in a single lipid bilayer that contain hydrogen peroxide-producing oxidases and catalases to inactivate reactive molecules (for review, see Gerhardt, 1992; Kindl, 1993; Olsen, 1998; Tabak et al., 1999). Arabidopsis and other oilseed plants ␤-oxidize longchain fatty acids (LCFAs) in peroxisomes to provide energy during germination. Plant peroxisomes also contain enzymes that act in photorespiration (Olsen, 1998) and the catabolism of branched-chain amino acids (Gerhardt, 1992; Zolman et al., 2001). In addition, seedlings and senescing tissues contain specialized peroxisomes called glyoxysomes that convert acetyl-coenzyme A (CoA) to succinate, which is transported to the mitochondria where it fuels the tricarboxylic acid cycle (Gerhardt, 1992; Olsen, 1998).Mammals metabolize fatty acids in both mitochondria and peroxisomes, and each organelle shortens a distinct subset of fatty acids (Lazarow, 1993; Tabak et al., 1999). In contrast, plants and yeast catabolize fatty acids exclusively in peroxisomes (Gerhardt, 1992; Kindl, 1993). Because peroxisomes lack DNA, proteins required for ␤-oxidation and other peroxisomal processes are translated in the cytoplasm and then imported (Olsen, 1998;Subramani, 1998; Tabak et al., 1999). Peroxisomal matrix proteins contain one of two peroxisomal targeting signals (PTSs). The PTS1 is made up of the amino acids "SKL" (or a conserved variant) at the extreme C termini of peroxisomal matrix-bound proteins (Gould et al., 1989). The PEX5 recept...

On the role of a Lipid-Transfer Protein. Arabidopsis ltp3 mutant is compromised in germination and seedling growth.

“…35 In A. thaliana, 3 independent experimental approaches have identified the same peroxisomal transporter, named CTS /PXA1/PED3, as responsible for the translocation of at least part of the fatty acids for b-oxidation. 31,38,39 It has been suggested that CTS /PXA1/PED3 might not be the only transporter for b-oxidation substrates into the peroxisome 34 and a LTP may be reasonable implicated in this process. A mayor concern to consider this hypothesis is the subcellular location of LTP3.…”

The SUGAR-DEPENDENT1 Lipase Limits Triacylglycerol Accumulation in Vegetative Tissues of Arabidopsis

“…Lipid metabolism in Arabidopsis roots and stems has received rather less attention than in leaves (LiBeisson et al, 2013). Our analysis of the pxa1 mutant, which is severely deficient in fatty acid b-oxidation (Zolman et al, 2001), showed that it also accumulates TAG in its roots. This suggests that b-oxidation does make a detectable contribution to the bulk turnover of fatty acid from membrane lipids in this tissue under normal growth conditions.…”

“…PXA1 is a peroxisomal ATPbinding cassette transporter that is required for fatty acid import for b-oxidation (Zolman et al, 2001), and CGI58 is an enzyme that has been reported to have lipase, phospholipase, and lysophosphatidic acid acyltransferase activities (Ghosh et al, 2009). Analysis of TAG content in pxa1-1 and cgi58-1 roots showed that both accumulated TAG, but not as much as sdp1-5 (Fig.…”

“…Among these are pxa1 (peroxisomal ABC transporter1) and cgi58 (comparative gene identification-58), which are associated with lipid catabolism. PXA1 is a peroxisomal ATP-binding cassette transporter that is required for fatty acid import for b-oxidation (Zolman et al, 2001), and CGI58 is a protein that has intrinsic lipase, phospholipase, and lysophosphatidic acid acyltransferase activities (Ghosh et al, 2009).…”

Peroxisome Function, Biogenesis, and Dynamics in Plants

“…Indole-3-butyric acid (IBA), one of several auxin precursors in plants (for review, see Korasick et al, 2013), is converted in peroxisomes to the active auxin indole-3-acetic acid (IAA; Zolman et al, 2000;Strader et al, 2010;reviewed in Strader and Bartel, 2011). IBA-derived auxin is important during seedling development, when it influences lateral rooting (Zolman et al, 2001;De Rybel et al, 2012), cotyledon and root hair expansion, and apical hook formation (Strader and Bartel, 2009;Strader et al, 2010.…”