An STS marker, Y202, located on the Silene latifolia Y chromosome between the chromosomal distal-end satellite DNA and SIY1

The pseudoautosomal region (PAR) is the chromosomal region where XY sex-chromo-some pairing occurs. The boundary of the PAR delineates the XY pairing and non-pairing regions, but detailed information about this region is lacking. In this study, we analyzed the sequences adja-cent to SlX1 and SlY1 in the dioecious plant Silene latifolia. SlX1 and SlY1, which are linked to the X and Y sex chromosomes, respectively, are thought to be closely linked to the PAR. The Sl-distal-satDNA is a satellite DNA found at the ends of S. latifolia chromosomes. The chromosomal distance between SlX1/SlY1 and Sl-distal-satDNA has not been examined. It was probably almost entire the PAR. However, the region between SlY1 and the Sl-distal-satDNA could be amplified in PCR. The nucleotide sequence between SlY1 and the Sl-distal-satDNA was determined following PCR amplification and compared to the sequence adjacent to SlX1 using BAC clones. In addition, a new male-specific STS marker, Y202, was designed based on the sequence adjacent to SlY1. Y202 as well as SlY1 were mapped on the Y chromosome using a panel of deletion mutants and FISH analysis. Our data suggest that the sequences adjacent to SlX1 and SlY1 do not simply follow a gradient of sequence divergence, a feature that was thought to allow the functioning of the PAR boundary. Therefore, recombination suppression in the XY chromosomes probably occurs via other mechanisms.