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.
Lange
Peter R
PR
Department of Biology, CNAP, Area 7, University of York, Heslington, York YO10 5YW, UK.
Eastmond
Peter J
PJ
Madagan
Kathryn
K
Graham
Ian A
IA
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