Nicotiana Chloroplast GenomeⅢ.Chloroplast DNA Evol...
Summary
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，SmaI，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.(https://www.daowen.com)
Key words：Nicotiana-Chloroplast DNA-Restriction fragments-Deletion-Evolution
