Metabolism of phenolic natural compounds at the threshold to life on land

从水生生活方式转变为陆地生活方式的植物会遇到各种生物（病原体，食草动物）和非生物（紫外线照射，水分流失）的压力，这些压力可以在酚类化合物的帮助下克服，酚类化合物具有抑制或抗生素以及吸收紫外线的特性，或者被纳入亲脂屏障。酚类化合物生物合成的基础是苯丙氨酸途径，它通过苯丙氨酸解氨酶（PAL）、肉桂酸4-羟化酶（C4H）和4-香豆酸辅酶a连接酶（4CL）三种酶的作用，由l -苯丙氨酸或l -酪氨酸形成活化的羟基肉桂酸。然后，在羟基肉桂酰基转移酶（HCT）、细胞色素P450单加氧酶（CYP98）和咖啡酰基shikimate酯酶（CSE）的参与下，4-Coumaroyl-CoA进一步代谢为单木脂醇和羟基肉桂酸酯/酰胺。所有这些酶在种子植物中都是众所周知的，但我们对早期分化的陆地植物或藻类中的酶的了解要有限得多。在第一个资助期，我们主要以苔藓植物Anthoceros agrestis、Marchantia polymorpha和Physcomitrium patens为模式生物，研究现存最早的陆地植物成员的上述基因和酶。此外，本文还对该性状的绿藻进行了一定程度的研究。从这些植物中选择感兴趣的酶基因序列，进行异源表达和生化表征。结果表明，苔藓植物数据库中的注释基本正确，其生化特征与种子植物中相应酶的生化特征相似。这对Chara braunii来说是不同的。首先，利用种子植物序列作为诱饵不容易识别基因；其次，注释往往不正确或令人困惑。这向我们表明，重要的是要关注藻类模式系统，以跟踪基因/酶的进化，因为这种进化可能已经发生。因此，除了Chara braunii，我们将集中研究另一种藻类模式生物，Mesotaenium endlicherianum (Zygnematophyceae)，以寻找酚代谢基因/酶的存在并表征编码酶的特征。对布氏查拉菌和恩氏中代菌基因组数据库的初步检查表明，我们的靶基因鉴定更为繁琐，必须考虑其他生物合成途径。

Plants changing from an aquatic to a terrestrial lifestyle encounter various biotic (pathogens, herbivores) and abiotic (UV irradiation, loss of water) stresses which can be overcome with help of phenolic compounds that have deterring or antibiotic as well as UV-absorbing properties or are incorporated into lipophilic barriers. The basis for the biosynthesis of phenolic compounds is the phenylpropanoid pathway which forms an activated hydroxycinnamic acid from L-phenylalanine or L-tyrosine by the action of three enzymes: phenylalanine ammonia-lyase (PAL), cinnamate 4-hydroxylase (C4H) and 4-coumarate CoA-ligase (4CL). 4-Coumaroyl-CoA then is further metabolized to monolignols and hydroxycinnamic acid esters/amides under participation of hydroxycinnamoyltransferases (HCT), cytochrome P450 monooxygenases (CYP98) and caffeoylshikimate esterases (CSE). All these enzymes are well known in seed plants, but our knowledge on them in early diverged land plants or algae is much more limited. In the first funding period, our main focus was on the above-mentioned genes and enzymes in extant members of the earliest land plants using the bryophytes Anthoceros agrestis, Marchantia polymorpha and Physcomitrium patens as model organisms. Chara braunii as green alga of the Characeae was also investigated to some extent. Gene sequences from these plants for the enzymes of interest were selected, heterologously expressed and biochemically characterized. Generally, our results showed that annotations in the bryophyte databases are mostly correct and the biochemical characteristics are similar to those of the respective enzymes from seed plants. This was different for Chara braunii. Here, firstly genes can not be identified as easily using seed plant sequences as baits, and secondly, the annotations often are not correct or confusing. This shows us, that it is important to concentrate on the algal model systems to follow the evolution of genes/enzymes of the phenylpropanoid pathway as organisms where this evolution might have occurred. Besides Chara braunii, we will therefore concentrate on another algal model organism, Mesotaenium endlicherianum (Zygnematophyceae), to look there for the presence of genes/enzymes of phenolic metabolism and to characterize the encoded enzymes. First inspections of Chara braunii and Mesotaenium endlicherianum genome databases have shown that the identification of our target genes is more tedious and alternative biosynthetic pathways must be taken into consideration.