Cytoplasmic male sterility (CMS) in Lolium perenne L. 2. The mitochondrial genome of a CMS line is rearranged and contains a chimaeric atp 9 gene.

The most striking difference between the mtDNAs of the fertile L. perenne line LPSB21 and the male-sterile line CMS9B290, is the presence in the former and the absence in the latter of a 5.6-kb HindIII fragment. This difference between fertile and sterile lines was the starting point for a detailed molecular analysis of the mitochondrial genome in the region spanning the 5.6-kb HindIII fragment in fertile L. perenne and the corresponding region in CMS9B290. Restriction mapping and Southern-blot analyses indicated that rearrangement of the mitochondrial genome consistent with a deletion/insertion event had occurred in the sterile line. Nucleotide-sequence analysis of the rearranged region in CMS9B290 revealed the presence of (1) a novel chimaeric gene, orf-C9, comprising the first six codons of atp9 fused to a further 118 codons of an unknown sequence and (2) a truncated version of an open reading frame, orf-L, originally identified in LPSB21 mtDNA. Northern-blot analysis confirmed the absence of orf-L transcripts and the presence of orf-C9 transcripts in the mtRNA of CMS9B290.