A. Kenton et al., CHARACTERIZATION OF THE NICOTIANA-TABACUM-L GENOME BY MOLECULAR CYTOGENETICS, MGG. Molecular & general genetics, 240(2), 1993, pp. 159-169
Nicotiana tabacum (2n = 48) is a natural amphidiploid with component g
enomes S and T. We used non-radioactive in situ hybridization to provi
de physical chromosome markers for N. tabacum, and to determine the ex
tant species most similar to the S and T genomes. Chromosomes of the S
genome hybridized strongly to biotinylated total DNA from N. sylvestr
is, and showed the same physical localization of a tandemly repeated D
NA sequence, HRS 60.1, confirming the close relationship between the S
genome and N. sylvestris. Results of dot blot and in situ hybridizati
ons of N. tabacum DNA to biotinylated total genomic DNA from N. toment
osiformis and N. otophora suggested that the T genome may derive from
an introgressive hybrid between these two species. Moreover, a compari
son of nucleolus-organizing chromosomes revealed that the nucleolus or
ganizer region (NOR) most strongly expressed in N. tabacum had a very
similar counterpart in N. otophora. Three different N. tabacum genotyp
es each had up to 9 homozygous translocations between chromosomes of t
he S and T genomes. Such translocations, which were either unilateral
or reciprocal, demonstrate that intergenomic transfer of DNA has occur
red in the amphidiploid, possibly accounting for some results of previ
ous genetic and molecular analyses. Molecular cytogenetics of N. tabac
um has identified new chromosome markers, providing a basis for physic
al gene mapping and showing that the amphidiploid genome has diverged
structurally from its ancestral components.