Plant sex determination: epigenomics and genomics of evolving sex determining regions

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Having separate sexes is taken for granted as a natural condition in most animals, yet the majority of flowering plants are hermaphrodite. However, around 6% of flowering plants are dioecious (having separate sexes) and this has evolved multiple times, in many different lineages. Many economically important plants are, or were developed from, dioecious species (e.g. kiwi fruit, hops, hemp, grape, strawberry, spinach). The molecular mechanisms by which different plants achieve dioecy has been mysterious until recently. Now rapid progress is being made due to advances in genomics. Our previous work discovered the genes present in the sex-determining region of the genome (SDR) of poplar (cottonwoods; Populus spp.) and discovered sex-specific DNA alterations (methylation) on one of these genes. We are now in a position to build on these results. The long-term objective of this research program is to provide a new understanding of sex-determination mechanisms in plants and to provide new tools and methods that can be applied to any plant that is dioecious. Specifically, we will (1) complete the assembly of the SDR (currently misassembled in v.3 of the Populus genome) and fully characterize the patterns of sex-specific expression and sex-specific methylation in Populus; (2) Develop a protocol for rapid whole methylome scan of any dioecious species, as a gateway into sex determination; (3) extend these studies to new dioecious systems including willows (Salix) and seaberry (Hippophae). (4) Understand the role of methylation in the evolution of dioecy in plants generally; (5) Understand how the structure of the SDR interacts with processes such as speciation, interspecific hybridization and polyploidization. Dioecious species are important to Canada. Of the plants in this proposal polars are important plantation trees for the pulp and paper industry, willows are an important biomass and bioremediation crop, and seaberry is a rapidly developing neutraceutical crop for the prairie provinces. Through collaboration with Agriculture and Agrifood Canada (AAFC) our work will allow sex identification and sex manipulation, aiding plant breeding and agronomic practice.