title: Nicotiana chloroplast genome III. Chloroplast DNA evolution.
abstract: Nicotiana chloroplast genomes exhibit a high degree of diversity and a general similarity as revealed by restriction enzyme analysis. This property can be measured accurately by restriction enzymes which generate over 20 fragments. However, the restriction enzymes which generate a small number (about 10) of fragments are extremely useful not only in constructing the restriction maps but also in establishing the sequence of ct-DNA evolution. By using a single enzyme, Sma I, a elimination and sequential gain of its recognition sites during the course of ct-DNA evolution is clearly demonstrated. Thus, a sequence of ct-DNA evolution for many Nicotiana species is formulated. The observed changes are all clustered in one region to form a "hot spot" in the circular molecule of ct-DNA. The mechanisms involved for such alterations are mostly point mutations but inversion and deficiency are also indicated. Since there is a close correlation between the ct-DNA evolution and speciation in Nicotiana a high degree of cooperation and coordination betwen organellar and nuclear genomes is evident.
authors.affiliation: Department of Biological Sciences, University of Maryland, Baltimore County (UMBC), Catonsville, Md., USA.
authors.forename: S D
authors.initials: SD
authors.lastname: Kung
authors.forename: Y S
authors.initials: YS
authors.lastname: Zhu
authors.forename: G F
authors.initials: GF
authors.lastname: Shen