Relationships among Genome A, B, and C Revealed by FISH and CAPS

Abstract

Physical localization of repetitive DNA sequence from genome A (151 bp) was carried out on the chromosomes of the selected Brassica species by FISH (fluorescence in situ hybridization). The signals distributed on all the chromosomes of A (Brassica rapa, 2n=20) or C genome (B. oleracea, 2n=18). For B. juncea (AABB, 2n=36), the signals were found on all the chromosomes of genome A and the strength of signal varied among different chromosomes, while the chromosomes of genome B showed weak or no signals. FAE1 gene is a rate-limiting gene for erucic acid synthesis in Brassica. The genes from six Brassica species of U-triangule were cloned by PCR. These PCR products were digested with different restriction endonucleases. Mbo I and Msp I were found to produce informative CAPS patterns of FAE1 gene. Three diploids displayed different patterns, the pat-terns of genome A was very similar to that of genome C, while the patterns of genome B was the most diverged out of the patterns of the A and C genomes. Three amphidiploids generally exhibited additive patterns of the progenitors, but not strictly in all cases, indicating that rearrangements and recombinations did occur in the formation and evolution of amphidiploids. Genetic relation-ships among Brassica species could be demonstrated through CAPS analysis of FAE1 gene and FISH method when repetitive DNA sequence (not ribosomal RNA genes) was used as a probe.