Polyols in the green algal class Trebouxiophyceae (Chlorophyta) - biochemical profiling and molecular characterization of biosynthetic mechanisms for a phylogenetic-(chemo)taxonomical classification

虽然大多数藻类通常栖息在水生环境中，但绿色藻类纲Trebouxiophyceae的一些成员定居在陆地栖息地。该纲可以通过分子方法细分为小球藻、卵囊藻和Trebouxia谱系，后者主要由气地物种组成。与它们的水生亲戚相比，这些藻类通常暴露在更恶劣的环境条件下。合成核糖醇等多元醇的能力被认为是对它们具有挑战性的栖息地的生物化学适应，因为这些物质通常有助于干燥和其他胁迫耐受。然而，Trebouxiophyceae很少研究有关的胁迫代谢产物，其分子生物学仍然是专家之间的争论。关于多元醇在这一纲中的分布的知识实际上仅限于气陆分类群。因此：I.一个系统的生物化学分析多元醇的表达将澄清的问题，这些化合物是否代表一个系统发育（化学）分类性状或独立进化允许藻类水到陆地的过渡，在某些谱系。二.首次对Trebouxiophyceae中的多元醇合成酶和编码基因进行了研究。由于其完整的基因组序列刚刚公布，因此将选择Trebouxiophycean种Coccomyxa作为模式生物来鉴定核糖醇生物合成的基因。三.通过对核糖醇合成关键酶和基因的鉴定，评价其作为新的分子分类学标记的价值。研究结果将有助于正在进行的关于微藻物种概念的讨论。

Although most algae typically inhabit aquatic environments, some members of the green algal class Trebouxiophyceae colonize terrestrial habitats. The class can be subdivided by molecular approaches into the Chlorella-, Oocystis- and Trebouxia- lineages, the latter one consisting of mostly aeroterrestrial species. Compared to their aquatic relatives, these algae are generally exposed to much harsher environmental conditions. The capability to synthesize polyols such as ribitol is regarded as biochemical adaptation towards their challenging habitat as these substances generally contribute to desiccation and other stress tolerances. However, the Trebouxiophyceae are rarely studied concerning such stress metabolites, and their molecular phylogeny is still debated among experts. Knowledge about polyol distribution within this class is actually restricted to aeroterrestrial taxa. Therefore: I. A systematic biochemical profiling for polyol expression will clarify the question whether these compounds represent a phylogenetic-(chemo)taxonomical trait or evolved independently permitting algal water-to-land transitions in certain lineages. II. The enzymes and coding genes for polyol biosynthesis in the Trebouxiophyceae will be investigated for the first time. The Trebouxiophycean species Coccomyxa will be chosen as model organism to identify the genes for ribitol biosynthesis since its complete genome sequence has just been published. III. After identification of the key enzymes and genes for ribitol biosynthesis, its value as new molecular-taxonomical marker will be evaluated. The results will contribute to the ongoing discussion on species concepts for microalgae.