An Arabidopsis mutant disrupted in valine catabolism is also compromised in peroxisomal fatty acid beta-oxidation.
Characterisation of the Arabidopsis dbr5 mutant, which was isolated on the basis of 2,4-dichlorophenoxybutyric acid (2,4-DB) resistance, revealed that it is disrupted in the CHY1 gene. CHY1 encodes a peroxisomal protein that is 43% identical to the mammalian beta-hydroxyisobutryl-CoA hydrolase of valine catabolism. We show that 2,4-DB resistance and the associated sucrose dependent seedling growth are due to a large activity decrease of 3-ketoacyl-CoA thiolase, which is involved in peroxisomal fatty acid beta-oxidation. (14)C-feeding studies demonstrate that dbr5 and chy1 seedlings are reduced in valine catabolism. These data support the hypothesis that CHY1 plays a key role in peroxisomal valine catabolism and that disruption of this enzyme results in accumulation of a toxic intermediate, methacrylyl-CoA, that inhibits 3-ketoacyl-CoA thiolase activity and thus blocks peroxisomal beta-oxidation. We also show that CHY1 is repressed in seedlings grown on sugars, which suggests that branched chain amino acid catabolism is transcriptionally regulated by nutritional status.
Department of Biology, CNAP, Area 7, University of York, Heslington, York YO10 5YW, UK.
Peter R
PR
Lange
Peter J
PJ
Eastmond
Kathryn
K
Madagan
Ian A
IA
Graham
D015084:2,4-Dichlorophenoxyacetic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000378:metabolism; D001483:Base Sequence; D002874:Chromosome Mapping; D032461:Chromosomes, Plant / Q000235:genetics; D005227:Fatty Acids / Q000378:metabolism*; D007700:Kinetics; D008322:Mammals; D010084:Oxidation-Reduction; D020675:Peroxisomes / Q000378:metabolism*; D013869:Thiolester Hydrolases / Q000378:metabolism; D014633:Valine / Q000378:metabolism*
D029681:Arabidopsis Proteins; D005227:Fatty Acids; D015084:2,4-Dichlorophenoxyacetic Acid; D013869:Thiolester Hydrolases; C035908:3-hydroxyisobutyryl-CoA hydrolase; D014633:Valine; C004764:4-(2,4-dichlorophenoxy)butyric acid