Cytogenetic characterization and genome size of the medicinal plant Catharanthus roseus (L.) G. Don

BACKGROUND AND AIMS Catharanthus roseus is a highly valuable medicinal plant producing several terpenoid indole alkaloids (TIAs) with pharmaceutical applications, including the anticancer agents vinblastine and vincristine. Due to the interest in its TIAs, C. roseus is one of the most extensively studied medicinal plants and has become a model species for the study of plant secondary metabolism. However, very little is known about the cytogenetics and genome size of this species, in spite of their importance for breeding programmes, TIA genetics and emerging genomic research. Therefore, the present paper provides a karyotype description and fluorescence in situ hybridization (FISH) data for C. roseus, as well as a rigorous characterization of its genome size. METHODOLOGY The organization of C. roseus chromosomes was characterized using several DNA/chromatin staining techniques and FISH of rDNA. Genome size was investigated by flow cytometry using an optimized methodology. PRINCIPAL RESULTS The C. roseus full chromosome complement of 2n = 16 includes two metacentric, four subtelocentric and two telocentric chromosome pairs, with the presence of a single nucleolus organizer region in chromosome 6. An easy and reliable flow cytometry protocol for nuclear genome analysis of C. roseus was optimized, and the C-value of this species was estimated to be 1C = 0.76 pg, corresponding to 738 Mbp. CONCLUSIONS The organization and size of the C. roseus genome were characterized, providing an important basis for future studies of this important medicinal species, including further cytogenetic mapping, genomics, TIA genetics and breeding programmes.