Sex chromosomes

The existence and evolution of sex chromosomes is a basic question in evolutionary biology. While sex chromosomes in the majority of animal species are ancient, plant sex chromosomes have evolved relatively recently, making dioecious plants good models for the study of early steps of sex chromosome evolution. Silene latifolia (syn. Melandrium album or white campion) is the dioecious plant possessing heteromorphic sex chromosomes, X and Y. It formally resembles the mammalian type of sex determination since the gender is controlled by the dominant Y chromosome-linked genes present only in male individuals. Recent data on S. latifolia show that both the X and Y chromosomes harbour active genes, but that they are slightly divergent due to the genetic degeneration of alleles in the non-recombining region of the Y. Our laboratory is mainly focused on isolation and characterization of DNA sequences from S. latifolia sex chromosomes.

We have constructed X- and Y-specific libraries using DNA template obtained from nitrogen laser microdissected chromosomes. New sex-chromosome linked sequences are used for FISH mapping of S. latifolia and related Silene species in order to search for the sex chromosome homologues. We have recently improved FISH strategy for differentiating the sex chromosomes of S. latifolia by chromosome painting. This approach represents a quick tool to compare organization of plant genomes. We have also generated new sex linked markers by constructing and screening a sample bacterial artificial chromosome (BAC) library to look for appropriate FISH probes. We also study the roles of repetitive DNA sequences in the evolution of sex chromosomes. We follow accumulation of promiscuous DNA and tandem repeats on the Y chromosome. Our recent data indicate a new type of retrotransposons carrying tandem repeats that reveal a unique mechanism of tandem repeat amplification in the genomes. The results of our current research show that divergence of the sex chromosomes of S. latifolia is already in process and degeneration of the Y chromosome by accumulation of specific sequences has begun.