RRC ID 4826
Author Beaudoin F, Wu X, Li F, Haslam RP, Markham JE, Zheng H, Napier JA, Kunst L.
Title Functional characterization of the Arabidopsis beta-ketoacyl-coenzyme A reductase candidates of the fatty acid elongase.
Journal Plant Physiol.
Abstract In plants, very-long-chain fatty acids (VLCFAs; >18 carbon) are precursors of sphingolipids, triacylglycerols, cuticular waxes, and suberin. VLCFAs are synthesized by a multiprotein membrane-bound fatty acid elongation system that catalyzes four successive enzymatic reactions: condensation, reduction, dehydration, and a second reduction. A bioinformatics survey of the Arabidopsis (Arabidopsis thaliana) genome has revealed two sequences homologous to YBR159w encoding a Saccharomyces cerevisiae beta-ketoacyl reductase (KCR), which catalyzes the first reduction during VLCFA elongation. Expression analyses showed that both AtKCR1 and AtKCR2 genes were transcribed in siliques, flowers, inflorescence stems, leaves, as well as developing embryos, but only AtKCR1 transcript was detected in roots. Fluorescent protein-tagged AtKCR1 and AtKCR2 were localized to the endoplasmic reticulum, the site of fatty acid elongation. Complementation of the yeast ybr159Delta mutant demonstrated that the two KCR proteins are divergent and that only AtKCR1 can restore heterologous elongase activity similar to the native yeast KCR gene. Analyses of insertional mutants in AtKCR1 and AtKCR2 revealed that loss of AtKCR1 function results in embryo lethality, which cannot be rescued by AtKCR2 expression using the AtKCR1 promoter. In contrast, a disruption of the AtKCR2 gene had no obvious phenotypic effect. Taken together, these results indicate that only AtKCR1 is a functional KCR isoform involved in microsomal fatty acid elongation. To investigate the roles of AtKCR1 in postembryonic development, transgenic lines expressing RNA interference and overexpression constructs targeted against AtKCR1 were generated. Morphological and biochemical characterization of these lines confirmed that suppressed KCR activity results in a reduction of cuticular wax load and affects VLCFA composition of sphingolipids, seed triacylglycerols, and root glycerolipids, demonstrating in planta that KCR is involved in elongation reactions supplying VLCFA for all these diverse classes of lipids.
Volume 150(3)
Pages 1174-91
Published 2009-7
DOI 10.1104/pp.109.137497
PII pp.109.137497
PMID 19439572
PMC PMC2705042
MeSH Acetyltransferases / metabolism* Alcohol Oxidoreductases / genetics Alcohol Oxidoreductases / metabolism Alcohol Oxidoreductases / physiology* Arabidopsis / cytology Arabidopsis / enzymology* Arabidopsis / genetics Arabidopsis Proteins / genetics Arabidopsis Proteins / metabolism Arabidopsis Proteins / physiology* Endoplasmic Reticulum / metabolism Genetic Complementation Test Molecular Sequence Data Mutagenesis, Insertional Protein Isoforms / genetics Protein Isoforms / metabolism Protein Isoforms / physiology RNA Interference Seeds / genetics Seeds / growth & development
IF 6.305
Times Cited 70
Arabidopsis / Cultured plant cells, genes pst14731