[Cloning and evolutionary analysis of homologous sequences of SAMDC gene in Cruciferae]

S-adenosylmethionine decarboxylase activity (SAMDC) is a key enzyme involved in biosynthesis of the polyamines, viz. spermidine and spermine. In the present study, SAMDC gene analogues from 14 species of 6 genera in Cruciferae were obtained by PCR strategy using specific primers designed from conserved regions of SAMDC gene reported in the GenBank. The phylogenetic relationships of these species belonging to the family Cruciferae were investigated through comparison of the genes. Homologous sequences of SAMDC comparison indicated that the similarities among the genes at nucleotide and amino acid levels were over 87% and 90%, respectively. The differences in genes at nucleotide and amino acid levels between species ranged from 0.2 % to 10.1 % and 0.3% to 6.6%, respectively, while those between genera except Raphanus were 4.9 % to 13.6 % and 3.1 % to 10.3%, respectively. The differences of sequences of nucleotides and amino acids among genera were higher than those among species, and the differences of nucleotides sequences were higher than those of amino acids. The phylogenetic tree was thus constructed based on the alignment nucleotides sequences from Nei's genetic distances. The neighbor-joining (NJ) and minimum-evolution (ME) trees showed that Brassica was closely related to Raphanus, followed by Barbarea, Roripl Scop and Arabidopsis Heynh, but was remotely related to Capsella Medic. This research elucidated the relationship among crucifer species at nucleotide level, which could proved some help for the utilization of plant germplasms.