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

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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.