Abstract
BackgroundEukaryotic aldehyde dehydrogenases (ALDHs, EC 1.2.1), which oxidize aldehydes into carboxylic acids, have been classified into more than 20 families. In mammals, Family 2 ALDHs detoxify acetaldehyde. It has been hypothesized that plant Family 2 ALDHs oxidize acetaldehyde generated via ethanolic fermentation, producing acetate for acetyl-CoA biosynthesis via acetyl-CoA synthetase (ACS), similar to the yeast pathway termed the "pyruvate dehydrogenase (PDH) bypass". Evidence for this pathway in plants has been obtained from pollen.ResultsTo test for the presence of the PDH bypass in the sporophytic tissue of plants, Arabidopsis plants homozygous for mutant alleles of all three Family 2 ALDH genes were fed with 14C-ethanol along with wild type controls. Comparisons of the incorporation rates of 14C-ethanol into fatty acids in mutants and wild type controls provided direct evidence for the presence of the PDH bypass in sporophytic tissue. Among the three Family 2 ALDHs, one of the two mitochondrial ALDHs (ALDH2B4) appears to be the primary contributor to this pathway. Surprisingly, single, double and triple ALDH mutants of Arabidopsis did not exhibit detectable phenotypes, even though a Family 2 ALDH gene is required for normal anther development in maize.ConclusionThe PDH bypass is active in sporophytic tissue of plants. Blocking this pathway via triple ALDH mutants does not uncover obvious visible phenotypes.
Highlights
Eukaryotic aldehyde dehydrogenases (ALDHs, EC 1.2.1), which oxidize aldehydes into carboxylic acids, have been classified into more than 20 families
Identification of null mutants of the three Family 2 ALDH genes aldh2B4-1 and aldh2B7-1 T-DNA knockout alleles were identified from the Arabidopsis Knockout Facility at the University of Wisconsin. aldh2C4-1, aldh2C4-2, and aldh2B4-2 T-DNA knockout alleles were identified from the Salk Institute T-DNA insertion library database
Direct evidence for the presence of pyruvate dehydrogenase (PDH) bypass for acetylCoA biosynthesis An ideal experiment to directly test for the presence of the PDH bypass in plants would be to compare the differences between wild type and mutants of involved genes in the incorporation of 14C-pyruvate or 14C-acetaldehyde into acetyl-CoA in plants in which the PDH pathway has been blocked
Summary
Eukaryotic aldehyde dehydrogenases (ALDHs, EC 1.2.1), which oxidize aldehydes into carboxylic acids, have been classified into more than 20 families. It has been hypothesized that plant Family 2 ALDHs oxidize acetaldehyde generated via ethanolic fermentation, producing acetate for acetyl-CoA biosynthesis via acetylCoA synthetase (ACS), similar to the yeast pathway termed the "pyruvate dehydrogenase (PDH) bypass". Evidence for this pathway in plants has been obtained from pollen. Aldehyde dehydrogenases (ALDHs, EC 1.2.1) oxidize aldehydes into carboxylic acids, using NAD+ or NADP+ as a co-factor. As such ALDHs play an important role in detoxifying aldehydes that are generated endogenously or introduced from the environment. The molecular mechanisms associated with the restorer function of the rf2a gene remain to be resolved, several studies in maize and other species have provided clues as to the physiological functions of Family 2 ALDHs in plants
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