Sucrose rescues seedling establishment but not germination of Arabidopsis mutants disrupted in peroxisomal fatty acid catabolism

Abstract

). † These authors contributed equally to this work. SummaryThe Arabidopsis acyl-CoA oxidase (ACX) family comprises isozymes with distinct fatty acid chain-length specificities that together catalyse the first step of peroxisomal fatty acid b-oxidation. We have isolated and characterized T-DNA insertion mutants in the medium to long-chain (ACX1) and long-chain (ACX2) acyl-CoA oxidases, and show that the corresponding endogenous activities are decreased in the mutants. Lipid catabolism during germination and early post-germinative growth was unaltered in the acx1-1 mutant, but slightly delayed in the acx2-1 mutant, with 3-day-old acx2-1 seedlings accumulating long-chain acyl-CoAs. In acx1-1 and acx2-1, seedling growth and establishment in the absence of an exogenous supply of sucrose was unaffected. Seedlings of the double mutant acx1-1 acx2-1 were unable to catabolize seed storage lipid, and accumulated long-chain acyl-CoAs. The acx1-1 acx2-1 seedlings were also unable to establish photosynthetic competency in the absence of an exogenous carbon supply, a phenotype that is shared with a number of other Arabidopsis mutants disrupted in storage lipid breakdown. Germination frequency of the double mutant was significantly reduced compared with wild-type seeds. This was unaffected by the addition of exogenous sucrose, but was improved by dormancy-breaking treatments such as cold stratification and after-ripening. We show that the acx1-1, acx2-1 and acx1-2 acx2-1 double mutants and the ketoacyl-CoA thiolase-2 (kat2) mutant exhibit a sucrose-independent germination phenotype comparable with that reported for comatose (cts-2), a mutant in a peroxisomal ABC transporter which exhibits enhanced dormancy. This demonstrates an additional role beyond that of carbon provision for the b-oxidation pathway during germination or in dormant seeds.

The ABC Transporter PXA1 and Peroxisomal β-Oxidation Are Vital for Metabolism in Mature Leaves ofArabidopsisduring Extended Darkness

“…Two long-chain acyl-CoA Synthetases (LACS6 and LACS7), activating fatty acids inside peroxisomes by esterification with CoA, are essential for mobilization of storage lipids in seeds, since lacs6 lacs7 double mutants depend on external sucrose for successful seedling establishment (Fulda et al, 2002(Fulda et al, , 2004. Sucrose dependency for seedling establishment was also found in mutants of other peroxisomal genes, such as the acylCoA oxidase double mutant acx1 acx2 (Adham et al, 2005;Pinfield-Wells et al, 2005) and the keto-acyl thiolase mutant kat2 (ped1) (Hayashi et al, 1998;Germain et al, 2001), all core enzymes of b-oxidation. Moreover, mutants of the peroxisomal ABC-transporter PXA1 display the same dependence on sucrose for seedling establishment (Zolman et al, 2001), providing evidence for an essential function of PXA1 in b-oxidation (Footitt et al, 2002;Hayashi et al, 2002).…”

The Multifunctional Protein in Peroxisomal β-Oxidation

“…By channeling, the intermediates need not equilibrate with the bulk solvent but are immediately directed from one active site to the next. In plants, an indication of specific isozyme functions by reduced jasmonate formation in the AtACX1/AtACX5 double mutant (20) and other evidence for specific involvement of AtACX1 and AtKAT2 in jasmonate synthesis (21)(22)(23)(24) suggest that weak or transient protein-protein interactions and channeling could be mechanisms by which plants control the flow of metabolites through ␤-oxidation.…”

Antifungal activity of Saccharomyces cerevisiae peroxisomal 3-ketoacyl-CoA thiolase

“…Transcripts of 3-ketoacyl-CoA thiolase are induced by treatment with certain stresses, such as senescence (10), fruit ripening (11), and pathogen exposure (12). Interestingly, 3-ketoacyl-CoA thiolase mutant plants (kat2-1 and ped1) have abnormal peroxisome morphology, decreased jasmonate levels, germination sucrose deficiency (13)(14)(15)(16), delayed http://bmbreports.org The elution fraction containing the target peak (arrow) was separated by RP-HPLC using a C18 column. Detail purification procedures are described in Material and Methods.…”