Intraspecific variations of the cytoplasmic male sterility genes orf108 and orf117 in Brassica maurorum and Moricandia arvensis, and the specificity of the mRNA processing

Abstract

The mitochondrial gene orf108, which is co-transcribed with atp1 and causes cytoplasmic male sterility in Brassica crops, is widely distributed across wild species and genera of Brassicaceae. However, to date, intraspecific variations in the presence of orf108 have not yet been studied, and the mechanisms underlying the wide distribution of the gene remain unclear. We analyzed the presence and sequence variations of orf108 in two wild species, Brassica maurorum and Moricandia arvensis. After polymerase chain reaction amplification of the 5′ region of atp1 and the coding sequence of orf108, we determined the DNA sequences. Brassica maurorum and M. arvensis showed variations in the presence of orf108 or orf117 (orf108V117) both between and within accessions and were not fixed to the mitochondrial type with the male sterile genes. Sequencing of the amplicons showed that B. maurorum had orf108V117 instead of orf108. Sequencing also indicated mitochondrial heteroplasmy in the two species; in particular, in B. maurorum, one plant possessed both orf108 and orf108V117 sequences. These results suggest that substoichiometric shifting of mitochondrial genomes leads to the acquisition or loss of orf108. Furthermore, fertility restorer genes of the two species were involved in the processing of the mRNA of male sterility genes at different sites.