NUCLEAR GENES ASSOCIATED WITH A SINGLE BRASSICA CMS RESTORER LOCUS INFLUENCE TRANSCRIPTS OF 3 DIFFERENT MITOCHONDRIAL GENE REGIONS

Previous studies have shown that the mitochondrial orf224/atp6 gene re gion is correlated with the Polima (pol) cytoplasmic male sterility (C MS) of Brassica napus. We now extend this correlation by showing that the effects of nuclear fertility restoration on orf224/atp6 transcript s cosegregate with the pol restorer gene Rfp1 in genetic crosses. We a lso show, however, that the recessive rfp1 allele, or a very tightly l inked gene, acts as a dominant gene, designated Mmt (modifier of mitoc hondrial transcripts), in controlling the presence of additional small er transcripts of the nad4 gene and a gene possibly involved in cytoch rome c biogenesis. A common sequence, TTGTGG, maps immediately downstr eam of the 5' termini of both of the transcripts specific to plants wi th the Mmt gene and may serve as a recognition motif in generation of these transcripts. A similar sequence, TTGTTG, that may be recognized by the product of the alternate allele (or haplotype), Rfp1, is found within orf224 just downstream of the major 5' transcript terminus spec ific to fertility restored plants. Our results suggest that Rfp1/Mmt i s a novel nuclear genetic locus that affects the expression of multipl e mitochondrial gene regions, with different alleles or haplotypes exe rting specific effects on different mitochondrial genes.