de Vries Jan, de Vries Sophie, Slamovits Claudio H, Rose Laura E, Archibald John M
Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada.
Population Genetics, Heinrich-Heine University Düsseldorf, Düsseldorf, Germany.
Plant Cell Physiol. 2017 May 1;58(5):934-945. doi: 10.1093/pcp/pcx037.
The origin of land plants from algae is a long-standing question in evolutionary biology. It is becoming increasingly clear that many characters that were once assumed to be 'embryophyte specific' can in fact be found in their closest algal relatives, the streptophyte algae. One such case is the phenylpropanoid pathway. While biochemical data indicate that streptophyte algae harbor lignin-like components, the phenylpropanoid core pathway, which serves as the backbone of lignin biosynthesis, has been proposed to have arisen at the base of the land plants. Here we revisit this hypothesis using a wealth of new sequence data from streptophyte algae. Tracing the biochemical pathway towards lignin biogenesis, we show that most of the genes required for phenylpropanoid synthesis and the precursors for lignin production were already present in streptophyte algae. Nevertheless, phylogenetic analyses and protein structure predictions of one of the key enzyme classes in lignin production, cinnamyl alcohol dehydrogenase (CAD), suggest that CADs of streptophyte algae are more similar to sinapyl alcohol dehydrogenases (SADs). This suggests that the end-products of the pathway leading to lignin biosynthesis in streptophyte algae may facilitate the production of lignin-like compounds and defense molecules. We hypothesize that streptophyte algae already possessed the genetic toolkit from which the capacity to produce lignin later evolved in vascular plants.
陆地植物起源于藻类，这是进化生物学中一个长期存在的问题。越来越清楚的是，许多曾经被认为是“胚植物特有的”特征实际上可以在它们最亲近的藻类亲属——链形植物藻类中找到。苯丙烷类途径就是这样一个例子。虽然生化数据表明链形植物藻类含有类木质素成分，但作为木质素生物合成主干的苯丙烷类核心途径被认为是在陆地植物基部出现的。在这里，我们利用来自链形植物藻类的大量新序列数据重新审视这一假设。通过追踪木质素生物合成的生化途径，我们发现苯丙烷类合成所需的大多数基因以及木质素产生的前体在链形植物藻类中已经存在。然而，对木质素产生过程中关键酶类之一肉桂醇脱氢酶（CAD）的系统发育分析和蛋白质结构预测表明，链形植物藻类的CAD与芥子醇脱氢酶（SAD）更为相似。这表明链形植物藻类中导致木质素生物合成途径的终产物可能促进类木质素化合物和防御分子的产生。我们推测，链形植物藻类已经拥有了遗传工具包，后来维管植物中产生木质素的能力就是从这个工具包进化而来的。
