Génomique évolutive des chromosomes X et Y de Silene latifolia, une plante dioïque – siXY

Sex chromosomes are unusual chromosomes. They are the very important players in differences between men and women because of their role in sex determination and sexual dimorphism. Mutations on sex chromosomes are considered a major source of human genetic diseases, including developmental abnormalities and mental disorders. All this and the evolutionary history of XY chromosomes are interesting for the public as the success of books on that matter clearly shows. Sex chromosomes are a dramatic example of the effect of recombination on genome organization, one of the most important issues of evolutionary genomics. While the X chromosomes can recombine in females, the Y never recombines with the X (with the exception of small pseudoautosomal regions). In humans, the X contains about 1000 genes. By contrast, the human Y contains no more than 150 genes and is literally invaded by DNA repeats, which is why we call it a degenerate chromosome. Lack of recombination is clearly the major difference between Y and X and population genetics explains why this should lead to degeneration. After intensive research on human XY, we are beginning to understand why and how recombination has stopped between sex chromosomes and what were the consequences of this. However, data on other sex chromosomes systems are needed to see how general is the picture that we have from human sex chromosomes and because there are questions that we can hardly address with our sex chromosomes because they are too old (> 100 millions years old). This project is based on a group of a CNRS fellow (G. Marais) and two lecturers from the University of Lyon 1 (R. Tavares, S. Mousset), who work at the Laboratoire Biométrie et Biologie Evolutive. We want to focus on a dioecious plant with XY chromosomes: Silene latifolia. Silene sex chromosomes are young (~10 millions years old) and heteromorphic, which makes it unique by comparison with the known sex chromosomes systems. Both early events of XY evolution and ongoing degeneration – two important issues very difficult to address in the classical old XY systems such as humans XY – can be investigated with Silene sex chromosomes. S. latifolia has closely related species without XY, which is extremely useful for comparative analysis. Being a plant, S. latifolia is also interesting because it provides data on whether plant and animal sex chromosomes evolve similarly. Despite important discoveries made on Silene XY, progress on this model organism research has always been slower than classical animal XY because of restricted amount of data. Only 1-2 new Silene sex-linked genes were found every year since the discovery of the first Silene sex-linked gene pair in late 90's. But the situation has changed. Large amount of genomic and transcriptomic data are being obtained in this species now. Prof. Alex Widmer's group in Zurich, a very close collaborator of ours, has developed a BAC library with a 5X coverage, a 5000 ESTs library and cDNA microarrays. We propose to take advantage of these developments to perform large-scale analysis for the first time in Silene. We will address the following important questions: - Recombination suppression between Silene XY - The degeneration of Silene Y chromosome - The origin of Silene XY and sex-determining genes - The evolution of dioecy in Silene genus Among the groups working in Silene worldwide, we are probably the best possible group to analyse these new data since our department has got a 30 years old experience in bioinformatics with a vast range of tools locally available and excellent computing facilities (http://pbil.univ-lyon1.fr/). Our main request is a 2 years postdoctoral position for analysing the new data and doing theoretical work to help interpret it. This would allow us to deal with the new genomic and transcriptomic resources in Silene quickly at this key time for Silene research. For the reasons mentioned above, Silene XY chromosomes could enable us to address questions that we can hardly address with classical animal systems including humans in a near future. This could provide significant advances in understanding sex chromosomes biology, which is of great interest given the importance of these chromosomes in basic science and biomedical research.