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生活在水生环境中，但绿藻类Trebouxiophyceae的一些成员定居在陆地栖息地。该类可以通过分子方法细分为小球藻、卵囊藻和Trebouxia谱系，后者主要由气陆物种组成。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。合成多元醇（如梨糖醇）的能力被认为是对其具有挑战性的栖息地的生化适应，因为这些物质通常有助于干燥和其他抗逆性。然而，关于这类应激代谢物的研究很少，其分子系统发育在专家中仍有争议。关于这类多元醇分布的知识实际上仅限于空陆分类群。因此：1 .多元醇表达的系统生化分析将澄清这些化合物是代表系统发育（化学）分类特征还是独立进化的问题，允许藻类在某些谱系中从水到陆地的过渡。2。本文首次研究了海藻科植物多元醇生物合成的酶和编码基因。我们将选择trebouxiophyceia物种Coccomyxa作为鉴定利比醇生物合成基因的模式生物，因为它的全基因组序列刚刚公布。3。对利比醇生物合成的关键酶和基因进行鉴定后，评价其作为新的分子分类标记的价值。这些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.