Periodic Reporting for period 2 - SuperGenE (Supergene evolution in a classic plant system - bringing the study of distyly into the genomic era)
Reporting period: 2019-07-01 to 2020-12-31
Distyly is an iconic floral polymorphism that ensures outcrossing and efficient pollen transfer to compatible plants. Distyly signifies the presence of two floral morphs, where flowers of different individuals differ reciprocally in the placement of male and female reproductive organs. Distyly has arisen independently many times in different evolutionary lineages, and is a textbook example of convergent evolution. It has been known for a long time that distyly is governed by a supergene, but until recently, the molecular makeup or evolution of distyly supergenes had not been studied in detail.
In this project, we aim to make full use of the latest advances in genomics to elucidate the evolution of a classic supergene that governs distyly in Linum, wild flaxseed species. This system is ideal for this purpose due to the dynamic nature of distyly in Linum. We will establish a genomic framework for studies of the evolution and loss of distyly in wild Linum by generating high-quality contiguous genome assemblies of six Linum species. We will then use these assemblies as a basis for identifying the characterizing the supergene that underlies distyly, and investigate supergene evolution at the genetic and regulatory level. Finally, we will investigate how and when distyly has been lost, and what the population genomic effects are.
The high-quality genomes produced in this project will pave the way for further studies to elucidate the molecular genetics of distyly, an adaptive floral polymorphism studied already by Darwin. The results are of general importance for an improved understanding of the evolution of coadapted gene complexes, and will shed new light on the fascinating phenomenon of supergenes.
We have used population resequencing data coupled with our high-quality assemblies to identify the supergene that governs distyly in Linum (the distyly S-locus). To assess how supergene genetic architecture affects evolutionary trajectories at supergenes such as the S-locus, we have conducted forward population genetic simulations. Our results suggest that the genetic architecture of supergenes has major consequences for the expected evolution of S-locus haplotypes. Extending these studies to other distylous and homostylous Linum species will allow further insights into the evolution and loss of distyly.
By the end of the project we thus expect to have generated additional Linum high-quality genome assemblies, using the methods we have established so far. We expect to have undertaken molecular evolution and gene expression studies to achieve an improved understanding of the evolutionary trajectories of supergene haplotypes. Finally, we expect to have an improved understanding of the genetic basis and population genomic consequences of loss of distyly, based on a combination of genome assembly and population genomics analyses in homostylous Linum species. Taken together, the results generated in this project are likely to be important for an improved understanding of the evolution of plant mating systems and the evolution of a classic supergene.