Requirement for 3‐ketoacyl‐CoA thiolase‐2 in peroxisome development, fatty acid β‐oxidation and breakdown of triacylglycerol in lipid bodies of Arabidopsis seedlings

Abstract

Summary 3-ketoacyl-CoA thiolase (KAT) (EC: 2.3.1.16) catalyses a key step in fatty acid b-oxidation. Expression of the Arabidopsis thaliana KAT gene on chromosome 2 (KAT2), which encodes a peroxisomal thiolase, is activated in early seedling growth. We identi®ed a T-DNA insertion in this gene which abolishes its expression and eliminates most of the thiolase activity in seedlings. In the homozygous kat2 mutant, seedling growth is dependent upon exogenous sugar, and storage triacylglycerol (TAG) and lipid bodies persist in green cotyledons. The peroxisomes in cotyledons of kat2 seedlings are very large, the total peroxisomal compartment is dramatically increased, and some peroxisomes contain unusual membrane inclusions. The size and number of plastids and mitochondria are also modi®ed. Long-chain (C16 to C20) fatty acyl-CoAs accumulate in kat2 seedlings, indicating that the mutant lacks long-chain thiolase activity. In addition, extracts from kat2 seedlings have signi®cantly decreased activity with aceto-acetyl CoA, and KAT2 appears to be the only thiolase gene expressed at signi®cant levels during germination and seedling growth, indicating that KAT2 has broad substrate speci®city. The kat2 phenotype can be complemented by KAT2 or KAT5 cDNAs driven by the CaMV 35S promoter, showing that these enzymes are functionally equivalent, but that expression of the KAT5 gene in seedlings is too low for effective catabolism of TAG. By comparison with glyoxylate cycle mutants, it is concluded that while gluconeogenesis from fatty acids is not absolutely required to support Arabidopsis seedling growth, peroxisomal b-oxidation is essential, which is in turn required for breakdown of TAG in lipid bodies.

Proteomic Study of Low-Temperature Responses in Strawberry Cultivars (Fragaria×ananassa) That Differ in Cold Tolerance

“…Three of the four different aldo-keto reductases identified, corresponding to spots 5318, 5439, and 5507, were at higher levels in 'Jonsok' and also demonstrated cold induction. 3-KetoacylCoA thiolase has a role in peroxisome morphology, and has potential role for redox control of peroxisomal fatty acid b-oxidation (Germain et al, 2001). One of the two 3-ketoacyl-CoA thiolases (spot 6539) reached a 10-fold-higher level in 'Jonsok' at 42 d due to a significant decrease in 'Frida'.…”

Gene-Specific Involvement of β-Oxidation in Wound-Activated Responses in Arabidopsis

“…The Arabidopis genome (Arabidopsis Genome Initiative [AGI], 2000), includes six genes encoding ACXs, ACX1 and ACX2 (Hooks et al, 1999); ACX3 (Eastmond et al, 2000;Froman et al, 2000); ACX4 (Hayashi et al, 1999); and the still uncharacterized homologs of ACX1 and ACX3, which we have named ACX1.2, and ACX3.2 (ACX5 and ACX6, respectively, in Rylott et al, 2003); at least two MFPs, AIM1 and MFP2 (Richmond and Bleecker, 1999); and three KATs, PED1/KAT2 (Hayashi et al, 1998;Germain et al, 2001), PKT2/KAT5 (Germain et al, 2001), and KAT1, a homolog of PED1/KAT2 in chromosome 1. Although b-oxidation has been traditionally considered as a catabolic machinery devoted to the production of energy through fatty acid degradation, it can be also considered as a processing system to convert complex precursors into simpler molecules.…”

The Peroxisome Deficient Arabidopsis Mutant sse1 Exhibits Impaired Fatty Acid Synthesis

“…Although unexpected from the role of peroxisomes/glyoxysomes in fatty acid catabolism, b-oxidation activity can be detected in developing Arabidopsis seeds where net fatty acid synthesis occurs (Arai et al, 2002). More intriguingly, a loss-of-function mutation in the Arabidopsis b-oxidation enzyme 3-ketoacyl-CoA thiolase causes reduced seed oil content (Germain et al, 2001). These observations raise the question as to whether peroxisomal b-oxidation contributes to lipid synthesis, in addition to its obvious function in the degradation process.…”