Rubio Silvia, Larson Tony R, Gonzalez-Guzman Miguel, Alejandro Santiago, Graham Ian A, Serrano Ramón, Rodriguez Pedro L
Instituto de Biología Molecular y Celular de Plantas, Universidad Politécnica de Valencia-Consejo Superior de Investigaciones Científicas, Spain.
Plant Physiol. 2006 Mar;140(3):830-43. doi: 10.1104/pp.105.072066. Epub 2006 Jan 13.
Once the plant coenzyme A (CoA) biosynthetic pathway has been elucidated by comparative genomics, it is feasible to analyze the physiological relevance of CoA biosynthesis in plant life. To this end, we have identified and characterized Arabidopsis (Arabidopsis thaliana) T-DNA knockout mutants of two CoA biosynthetic genes, HAL3A and HAL3B. The HAL3A gene encodes a 4'-phosphopantothenoyl-cysteine decarboxilase that generates 4'-phosphopantetheine. A second gene, HAL3B, whose gene product is 86% identical to that of HAL3A, is present in the Arabidopsis genome. HAL3A appears to have a predominant role over HAL3B according to their respective mRNA expression levels. The hal3a-1, hal3a-2, and hal3b mutants were viable and showed a similar growth rate as that in wild-type plants; in contrast, a hal3a-1 hal3b double mutant was embryo lethal. Unexpectedly, seedlings that were null for HAL3A and heterozygous for HAL3B (aaBb genotype) displayed a sucrose (Suc)-dependent phenotype for seedling establishment, which is in common with mutants defective in beta-oxidation. This phenotype was genetically complemented in aaBB siblings of the progeny and chemically complemented by pantethine. In contrast, seedling establishment of Aabb plants was not Suc dependent, proving a predominant role of HAL3A over HAL3B at this stage. Total fatty acid and acyl-CoA measurements of 5-d-old aaBb seedlings in medium lacking Suc revealed stalled storage lipid catabolism and impaired CoA biosynthesis; in particular, acetyl-CoA levels were reduced by approximately 80%. Taken together, these results provide in vivo evidence for the function of HAL3A and HAL3B, and they point out the critical role of CoA biosynthesis during early postgerminative growth.
一旦通过比较基因组学阐明了植物辅酶A（CoA）的生物合成途径，分析CoA生物合成在植物生命中的生理相关性就变得可行。为此，我们已经鉴定并表征了两个CoA生物合成基因HAL3A和HAL3B的拟南芥（Arabidopsis thaliana）T-DNA敲除突变体。HAL3A基因编码一种4'-磷酸泛酰巯基乙胺脱羧酶，可生成4'-磷酸泛酰巯基乙胺。第二个基因HAL3B，其基因产物与HAL3A的基因产物有86%的同一性，存在于拟南芥基因组中。根据它们各自的mRNA表达水平，HAL3A似乎比HAL3B起主要作用。hal3a-1、hal3a-2和hal3b突变体是有活力的，并且显示出与野生型植物相似的生长速率；相比之下，hal3a-1 hal3b双突变体胚胎致死。出乎意料的是，HAL3A缺失且HAL3B杂合（aaBb基因型）的幼苗在幼苗建立方面表现出蔗糖（Suc）依赖性表型，这与β-氧化缺陷的突变体相同。这种表型在后代的aaBB同胞中通过遗传互补得到补充，并通过泛硫乙胺进行化学互补。相比之下，Aabb植物的幼苗建立不依赖于蔗糖，这证明了在此阶段HAL3A比HAL3B起主要作用。对缺乏蔗糖的培养基中5日龄aaBb幼苗的总脂肪酸和酰基辅酶A测量显示，储存脂质分解代谢停滞，CoA生物合成受损；特别是，乙酰辅酶A水平降低了约80%。综上所述，这些结果为HAL3A和HAL3B的功能提供了体内证据，并指出了CoA生物合成在种子萌发后早期生长过程中的关键作用。
