Molecular analysis of cytoplasmic male sterility in beets

To study the molecular basis of cytoplasmic male sterility (CMS) in sugarbeet we have conducted a detailed comparison of the mitochondrial genomes of two sugarbeet lines, one containing a fertile (N) cytoplasm and the other a male sterile one (the 'Owen' cytoplasm). The two genomes are 369kb and 482kb long, for N and Owen-CMS, respectively. They have approximately 330kb of common sequences but there is considerable variation in sequence organization which can be accounted for genome rearrangements. Transcripts and translation products for known mitochondrial genes and regions of the two sugarbeet genomes known to be rearranged relative to each other were compared among male-fertile, CMS and nuclear-restored sugarbeet genotypes. Our results suggest that the 5' flanking sequence of atp6 is most likely to be involved in the expression of CMS. Bulked segregant analysis was utilized to identify AFLP markers linked to the fertility restorer gene(s) in sugarbeet. The restorer locus is now flanked by AFLP markers within a genetic window of 3.4cM.