Chromosomal Localization Of 5s And 18s Rdna In Eight Nicotiana Species And The Implications For Genome Evolution Of Genus Nicotiana

Studying the genome evolution of Nicotiana has been hindered by the small chromosome and complex chromosomal number. Consequently, studying the chromosomal structure is a very important work in clarifying the genome evolution of genus Nicotiana. In the present study, the 18S and 5S rDNA sites of eight Nicotiana species were physically mapped by double-probe FISH. Results showed the following: 1) each species (including the S-genome and T-genome of N. tabacum) had one or two pairs of 5S rDNA sites and chromosome VIII of each species had one pair of 5S rDNA sites in the interstitial region of the long arm; 2) each species (including the S-genome and T-genome of N. tabacum) had one, two or three pairs of 18S rDNA sites; 3) the chromosomal distribution of 5S and 18S rDNA was same between N. setchellii, N. kawakamii and N. otophora, and between N. glutinosa and N. tomentosa; and the chromosomal distribution of 5S and 18S rDNA of N. sylvstris and N. tomentosiformis was same with the S-genome and T-genome of N. tabacum, respectively. Finally, the genome evolutions of the genus Nicotiana were inferred. The present results could provide obvious references for studies on the system and phylogenesis of genus Nicotiana and were of significance to genetic breeding and germplasm innovation for tobacco.