Abstract:  Nsa cytoplasmic male sterility (CMS) is a novel CMS system develpoed by somatic hybridization between Brassica napus and Sinapis arvensis. The cloning the restorer genes for Nsa CMS is important for both the development of better restorers and the mechanism understanding of fertility restoration. A candidate restorer gene named PPR618 of Nsa CMS was cloned based on the homologue sequencing strategy previously. In this study, based on sequence information of PPR618, 22 homologous sequences were identified in Nsa CMS male sterile line, Nsa CMS restorer lines, the original fusion parents which gave rise to Nsa CMS and several other B. napus lines as well as one B. oleracea and one B. rapa accessions. Sequence analysis showed that there are two PPR618 homologues in each of the fusion parental lines, S. arvensis var. Yeyou 18 and B. napus var. Zhongshuang 4, whereas there were three, one, one, and one PPR618 homologues in the four restorers, Hui 1, Hui 2, Hui 3, and Hui 4, respectively. The identity of the homologous genes in restorers was above 93% to those in Yeyou 18, but less than 80% to those in Zhongshuang 4, implicating the candidate restorer genes of Nsa CMS originated from S. arvensis. Both homologues in S. arvensis were found in the restorers, one in Hui1, Hui 3, and Hui 4, the other in Hui 2. Besides PPR618, three new candidate restoring genes were identified. The homologous genes from restorers was also found to have relations with the restoring genes for CMS system of radish and petunia. Semi-quantitative RT-PCR results showed that the candidate restoring gene expressed in all tested organs. The gene expression gradually increased along with the developmental process from vegetative to reproductive stages, peaked in the bud of 1.5–2.5 mm in diameter, and slumped in roots and stems. In contrast, the highest expression of homologous gene in male sterile line was detected in stems.

Key words: Nsa CMS, Restorer gene, Homologous sequence, Expression