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生环境的转变是地球上生命进化过程中最重要的事件之一。在陆地上，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。为了应对这些挑战，早期的陆地植物发展出了胞外基质，其中包括孢粉素、角质素和木质素。本研究项目旨在进一步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。苔藓植物包括苔类、苔藓类和角苔类，它们是陆地植物中最简单、分化最早的分支，为研究陆地植物的早期进化提供了独特的窗口。随着小壶藓（Physcomitrella patens）基因组序列的完整，它正迅速成为研究植物进化的模式苔藓植物。在小立壶菌中，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。我们的研究重点是孢粉素的生物合成，孢粉素是一种存在于孢子和花粉壁中的生物聚合物，以及植物III型聚酮合成酶（PKS）的进化，这些酶共同产生多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如何促进陆地植物的早期进化，并将阐明孢粉素生物合成的后期阶段。植物是如何制造细胞壁的，这是一个尚待解答的基本问题。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点，可用于杂交制种和林产控制。作为最坚固的生物聚合物，孢粉素在生物技术和医学上也有独特的应用。在本研究中获得的关于孢粉素生物合成途径的知识将有助于我们操纵孢粉素的生物合成。

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.