Identification, functional characterization and evolution of enzymes involved in secondary metabolism in the moss Physcomitrella patens

大约5亿年前，植物从水生环境过渡到陆地环境是地球生命进化中最重要的事件之一。一旦踏上陆地，早期的陆地植物面临着许多新的挑战，包括干燥，紫外线照射和重力。为了科普这些挑战，早期的陆地植物开发了孢粉素、角质和木质素的细胞外基质等。该研究项目旨在更多地了解这些保护性化合物的生物合成途径在早期陆地植物进化过程中是如何进化的。由地钱、苔藓和角苔组成的苔藓植物是陆地植物中最简单、最早分化的谱系，为了解陆地植物的早期进化提供了独特的窗口。拥有完整基因组序列的小立碗藓（Physcomitrella patens）正在迅速成为植物进化研究的模式苔藓植物。在小立碗藓中，可以有效地敲除靶基因，使研究人员能够研究靶基因的功能。我们的研究一直集中在孢粉素，在孢子和花粉壁中发现的生物聚合物的生物合成，并在植物III型聚酮酶（PKS）的进化，共同产生各种次生代谢产物具有不同的生理作用。使用多方面和跨学科的方法，我们将确定如何古老的III型PKSs有助于陆地植物的早期进化，也将阐明孢粉素生物合成的后期阶段。一个基本的问题仍然有待回答的是植物如何制造细胞壁。我们的研究应该有助于回答这个问题。孢粉素生物合成基因是产生植物雄性不育的良好靶标，用于杂交种子生产和森林/作物控制。作为最强大的生物聚合物，孢粉素在生物技术和医学方面也有独特的应用。在这项研究中获得的知识，对孢粉素的生物合成途径，应该是有用的操纵孢粉素的生物合成为我们的利益。

The transition of plants from aquatic to terrestrial environments about 500 million years ago is one of the most important events in the evolution of life on earth. Once on land, early land plants faced numerous new challenges including desiccation, UV irradiation, and gravity. In order to cope with these challenges, early land plants developed, among others, extracellular matrices of sporopollenin, cutin and lignin. This research program seeks to learn more about how the biosynthetic pathways for these protective compounds evolved during early land plant evolution. Bryophytes comprising liverworts, mosses, and hornworts are the simplest and earliest-diverging lineages of land plants, and offer unique windows into the early evolution of land plants. With a complete genome sequence, the moss Physcomitrella patens is rapidly emerging as a model bryophyte for research on plant evolution. In Physcomitrella patens, a target gene can efficiently be knocked out, allowing researchers to study function of the target gene. Our research has been focused on the biosynthesis of sporopollenin, a biopolymer found in spore and pollen walls, and on the evolution of plant type III polyketide synthases (PKS) that collectively produce a variety of secondary metabolites with different physiological roles. Using multi-faceted and interdisciplinary approaches, we will determine how ancient type III PKSs contributed to the early evolution of land plants, and will also elucidate the later stages of sporopollenin biosyntheses. One of the fundamental questions remain to be answered is how plants make cell walls. Our research should help answer this question. Sporopollenin biosynthetic genes are good targets to generate plant male sterility for hybrid seed production and forest/crop control. Being the most robust biopolymer, sporopollenin also has unique applications in biotechnology and medicine. Knowledge gained in this research on the biosynthetic pathways of sporopollenin should be useful in manipulating sporopollenin biosynthesis for our benefit.