ALLOPLASMIC MALE-STERILE BRASSICA LINES CONTAINING B-TOURNEFORTII MITOCHONDRIA EXPRESS AN ORF-3' OF THE ATP6 GENE AND A 32 KDA PROTEIN

Analyses of mitochondrial transcription and in organello translation w ere performed with the Brassica tournefortii cytoplasm. This cytoplasm causes alloplasmic male sterility when combined with the nuclear geno mes of B. napus and B. juncea. Mitochondrial RNA and protein banding p atterns were compared between the fertile wild species B. tournefortii , an alloplasmic male-sterile B. juncea line, an alloplasmic male-ster ile B. napus line and an alloplasmic B. napus line with restored ferti lity. The analyses were carried out to identify differences in gene ex pression and to investigate whether alterations in gene expression acc ompanied male sterility. A difference in transcription patterns betwee n the fertile B. tournefortii and the alloplasmic lines was found for the atp6 gene. The atp6 region was investigated further, since a simil ar alteration in atp6 transcription has been observed in two other Bra ssica cytoplasms which are associated with cytoplasmic male sterility (CMS). The additional longer atp6 transcript detected in the alloplasm ic lines in the present study was found to contain an open reading fra me (ORF) located downstream of the atp6 gene. DNA sequencing revealed that the ORF, orf263, could encode a protein with a predicted molecula r weight of about 29 kDa. In organello analysis detected two proteins, of 29 and 32 kDa respectively, which were found only in the alloplasm ic lines. Furthermore, the 32 kDa protein accompanied male sterility s ince it was absent in alloplasmic plants restored to fertility. The pr otein analysis might indicate that orf263 is translated and causes CMS .