Wei Yanling, Lin Ming, Oliver David J, Schnable Patrick S
Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA 50011, USA.
BMC Biochem. 2009 Mar 25;10:7. doi: 10.1186/1471-2091-10-7.
Eukaryotic 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.
To 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.
The PDH bypass is active in sporophytic tissue of plants. Blocking this pathway via triple ALDH mutants does not uncover obvious visible phenotypes.
真核生物醛脱氢酶（ALDHs，EC 1.2.1）可将醛氧化为羧酸，已被分为20多个家族。在哺乳动物中，第2家族醛脱氢酶可对乙醛进行解毒。据推测，植物第2家族醛脱氢酶可氧化乙醇发酵产生的乙醛，通过乙酰辅酶A合成酶（ACS）产生用于乙酰辅酶A生物合成的乙酸，类似于酵母中称为“丙酮酸脱氢酶（PDH）旁路”的途径。已从花粉中获得了植物中该途径的证据。
为了检测植物孢子体组织中是否存在PDH旁路，给所有三个第2家族醛脱氢酶基因突变体等位基因的纯合拟南芥植株饲喂14C-乙醇，并设置野生型对照。比较突变体和野生型对照中14C-乙醇掺入脂肪酸的速率，为孢子体组织中存在PDH旁路提供了直接证据。在三个第2家族醛脱氢酶中，两个线粒体醛脱氢酶之一（ALDH2B4）似乎是该途径的主要贡献者。令人惊讶的是，拟南芥的单、双和三醛脱氢酶突变体均未表现出可检测到的表型，尽管玉米正常花药发育需要一个第2家族醛脱氢酶基因。
PDH旁路在植物的孢子体组织中具有活性。通过三醛脱氢酶突变体阻断该途径并未发现明显的可见表型。
