CHARACTERIZATION AND EXPRESSION OF THE MITOCHONDRIAL GENOME OF A NEW-TYPE OF CYTOPLASMIC MALE-STERILE SUNFLOWER

A new cytoplasmic male sterile sunflower, CMS3 [44], was characterised in relation to the Petiolaris (PET1) cytoplasmic male-sterile sunflow er, CMS89 [25]. Southern blot analysis showed that the mitochondrial g enome of CMS3 contains unique rearrangements in at least five loci (at p6, atp9, atpA, nad1 + 5 and coxIII) compared to the PET1 sterile and the fertile cytoplasms. Transcripts of two (coxIII and atp6) of the fi ve rearranged loci differed in CMS3 when compared to the corresponding loci in the PET1 and fertile cytoplasms. In organello protein synthes is experiments showed that the ca. 15 kDa mitochondrial polypeptide, c haracteristic of PET1, is not present in the CMS3 line. These data sug gest that the molecular basis of male sterility in the CMS3 line diffe rs from that of the PET1 cytoplasm. The nucleotide sequences of the co ding and the immediate flanking regions of the coxIII and atp6 genes o f CMS3 were compared to the corresponding regions from the fertile sun flower. In CMS3 the ORFB-cox III locus is located immediately 3' to th e atpA gene whereas in the fertile cytoplasm these two loci are ca. 60 kb apart. This DNA rearrangement probably involved a 265 bp repeat wh ich may be implicated in the DNA recombination associated with PET1 CM S. The atp6 gene in CMS3 contains a 5'-terminal extention which result s in an extended ORF. The potential involvement of the rearrangements associated with the coxIII and atp6 loci in relation to the CMS phenot ype is discussed.