OPUS: CRS: Why do heterosporous plants have so few chromosomes?

University Of Alabama In Huntsville, Huntsville AL

Investigators

Abstract

Most plants, and including many crop species, have undergone an increase in the number of their chromosomes through a process called polyploidization. Polyploidization can yield new adaptive traits and promote species diversification, but it can also lead to genomic instability and infertility. This project will synthesize the principal investigator's long-term research on how plant genomes respond to polyploidization over evolutionary time. Synthesis activities will focus on characterizing the mechanisms responsible for the phenomenon of genome downsizing, whereby plants lose genetic material following polyploidization. The project will then compare this phenomenon among homosporous and heterosporous land plants to advance knowledge about the possible genesis of their divergent genome architectures. Heterosporous plants, which include all seed plants and some seedless ones, have several times fewer chromosomes on average than do homosporous plants, which include non-vascular plants as well as most ferns and lycophytes. Broader impacts will include the production of review papers to communicate the results of the synthetic work. Results from this research may help agronomists understand genome instability and infertility during polyploid crop development. Despite five decades of theory and experiments, a mechanistic explanation for why homosporous plants have higher chromosome numbers than heterosporous plants has remained elusive. Well-established phylogenetic relationships of land plants show that heterospory is the derived condition and that genome downsizing during meiosis bears close investigation as a possible cause of divergent genome architectures among these major groups of land plants. The principal investigator will place this long-standing research question in a broader context of genome dynamics in all plants. Synthetic activities will include: 1) a review of mechanisms of genome downsizing, with a focus on spindle formation and intergenomic translocation in diploid versus polyploid plant species; 2) comparative bioinformatic analyses of homosporous and heterosporous plant genomes to examine distribution of genes expressed during different stages of meiosis and especially those associated with spindle formation; 3) synthesis of data and theories into a comprehensive review of the relationship between homospory and chromosome number; and 4) design of the next phase of research to examine spindle formation and crossing-over behavior in homosporous and heterosporous plants. Outcomes of the work will provide a synthetic historical perspective on approaches to this research question and will advance the ability of future researchers to investigate plant genome evolution. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.