Poplar dioecy

Background and Objective

The separation of female and male flowers onto different individuals, called dioecy, has evolved independently hundreds if not thousands of times. Nevertheless, the underlying genetic basis remains mostly elusive. The principal theoretical model assumes two genetically linked mutations, one affecting male stamina, and one female carpel development (Charlesworth & Charlesworth, 1978). An intriguing alternative is a switch-like single-gene-based mechanism (Renner, 2016). However, such a single-gene-based mechanism has been difficult to unambiguously test.

In this project, we want to employ poplar natural variation, to resolve the genetic basis and the evolution of an ancient but genetically highly variable system of sex determination. We want to understand the impact of sex chromosomes on recombination (crossing over), determine the genes and gene variants ‚trapped‘ on the sex chromosomes, and identify possible secondary effects of dioecy. Finally, we want to experimentally test whether sex is determined by a single gene in poplars. The results are of fundamental scientific interest but also of great practical relevance.

Approach

In this project, we will combine genetic, genomic and biotechnological methods. Using classical experimental populations we want to precisely localize the sex-determining regions of aspen and white poplar. We further want to assess recombination frequencies along these regions. Genome sequences of various poplar individuals will allow us to have a detailed look into the genes and sequence motifs on the sex chromosomes. We will use publically available genomes but also generate new data, including third generation long read sequences using a MinION device. Finally, we will employ biotechnological methods, including CRISPR/Cas9, to experimentally test our hypotheses. The collective genetic, genomic and biotechnological amenability of poplar is absolutely unique among dioecious plant species and therefore offers truly exceptional possibilities for studying the genetics of dioecy.