Analysis of Chloroplast Genome of Two Cytoplasmic Male Sterile Lines Derived from Interspecific Chimera and Intergeneric Somatic Hybrid in Brassicaceae

Two new types of cytoplasmic male sterile (CMS) lines have been developed, one by in vitro chimera formation between Brassica rapa and B. oleracea and another by protoplast fusion of B. oleracea with Raphanus sativus. These CMS lines harbored an Ogura-type mitochondrial gene, orf138. They expressed chlorosis at a young stage and their chloroplast genome changed to the type of Ogura radish based on restriction fragment length polymorphism (RFLP) analysis. Thus, we attempted to study the relationships among cytoplasmic male sterility, chlorosis and the variation of the chloroplast genome using the matK and RuBisCO genes. The two CMS lines, normal and male sterile radishes exhibited similar matK gene sequences, while B. rapa and B. oleracea showed matK sequences of the radish type in very low copy numbers. The CMS lines displayed an identical RFLP pattern with that of the male sterile radish in the RuBisCO gene region. These phenomena indicated that the chloroplast genome organization had changed from Brassica to Raphanus type or Raphanus CMS type by CMS induction, and suggested the existence of heteroplasia in the Brassica chloroplast.