Physical Mapping of the 18S.26S RRNA Multigene Family in Mutant form ofS. LatifoliaL: Identification of a new Locus

Silene latifolia is a key plant model in the study of sex determination and sex chromosome evolution. Current studies have been based on fluorescent in situ hybridization (FISH). FISH in situ hybridization in conjucation with Ag-staining was used to map physically the 18S.26S multigene rRNA family in S. latifolia L. The 18S-5.8S-26S rRNA genes have been located on four pairs of Silene chromosomes. The pairs of majors rRNA sites on chromosome 5, 7, 9 and 10 are well known. Silver staining of nuclei and in situ hybridization analysis have previously indicated that additional rDNA sites may be present, but the presence of sites on a five chromosome pairs was unexpected. Using FISH in situ hybridization, we report a new fifth locous in S. latifolia and also confirm the nucleolus organizing region (Nor) by Ag-staining. We propose calling the new sites Nor-11. In situ hybridization is valuable for gene mapping, since it can detect presence of genes with a very wide range of copy number at different sites.