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向陆地环境的转变是地球生命进化中最重要的事件之一。一旦登上陆地，早期的陆地植物就面临着许多新的挑战，包括干燥、紫外线照射和重力。为了应对这些挑战，早期的陆地植物发展了孢粉、角质和木质素等胞外基质。这项研究计划试图了解更多关于这些保护性化合物的生物合成途径是如何在早期陆地植物进化过程中进化的。苔藓植物由苔藓、苔藓和角藻组成，是陆地植物中最简单和最早分化的谱系，为了解陆地植物的早期进化提供了独特的窗口。由于拥有完整的基因组序列，小立苔藓正在迅速崛起，成为研究植物进化的模式苔藓植物。在Physcomitrella patens中，可以有效地敲除目标基因，使研究人员能够研究目标基因的功能。我们的研究集中在孢粉蛋白的生物合成，以及植物III型聚酮合成酶(PKS)的进化，这些PKS共同产生各种具有不同生理作用的次生代谢产物。利用多方面和跨学科的方法，我们将确定古代III型PKS如何对陆地植物的早期进化做出贡献，并将阐明孢粉蛋白生物合成的后期阶段。有待回答的基本问题之一是植物如何形成细胞壁。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，可用于杂交制种和森林/作物控制。作为最强大的生物聚合物，孢粉蛋白在生物技术和医学中也有独特的应用。在这项研究中获得的有关孢粉蛋白生物合成途径的知识应该有助于我们操纵孢粉蛋白的生物合成。

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.