Sucrose rescues seedling establishment but not germination of Arabidopsis mutants disrupted in peroxisomal fatty acid catabolism.
The 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 beta-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 beta-oxidation pathway during germination or in dormant seeds.
Pinfield-Wells
Helen
H
CNAP, Department of Biology, University of York, PO Box 373, York YO10 5YW, UK.
Rylott
Elizabeth L
EL
Gilday
Alison D
AD
Graham
Stuart
S
Job
Kathleen
K
Larson
Tony R
TR
Graham
Ian A
IA
D000214:Acyl Coenzyme A / Q000378:metabolism; D042962:Acyl-CoA Oxidase / Q000235:genetics / Q000502:physiology; D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000502:physiology; D003517:Cyclopentanes / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism*; D018525:Germination / Q000187:drug effects*; D009154:Mutation; D054883:Oxylipins; D020675:Peroxisomes / Q000235:genetics / Q000378:metabolism; D036226:Seedlings / Q000187:drug effects*; D013395:Sucrose / Q000494:pharmacology*; D013997:Time Factors
D000214:Acyl Coenzyme A; D029681:Arabidopsis Proteins; D003517:Cyclopentanes; D005227:Fatty Acids; D054883:Oxylipins; D013395:Sucrose; C011006:jasmonic acid; C495584:ACX1 protein, Arabidopsis; C505728:ACX2 protein, Arabidopsis; D042962:Acyl-CoA Oxidase