Genetic variation of petaloid male-sterile cytoplasm of carrots revealed by sequence-tagged sites (STSs)

The mitochondrial DNA of various carrot lines was characterized by random amplified polymorphic DNA (RAPD) analysis, and six sequence-tagged sites (STSs) led to identification of the petaloid type of cytoplasmic male sterility (CMS). Using six STS primer combinations, we were able to classify five CMS lines into two groups and eight fertile carrots into six groups. Both the STS1 and the STS4 primer combinations differentiated CMS cytoplasms from the fertile cytoplasms, and the STS2 primer combination revealed two different types of CMS cytoplasms - of Wisconsin Wild and Cornell origins. Cybrid carrot lines with petaloid flowers which had been obtained by asymmetric cell fusion could also be separated from fertile cybrids by the STS1 primer combination. The STS1 fragment contained a homologous sequence with the orfB gene. DNA gel blot analysis indicated that homologous regions to the STS1 fragment existed in fertile types as well as the CMS types, although the restriction fragment size patterns differed. These observations demonstrate that rearrangements involving this region occurred in the mitochondrial genome. The STS4 fragment had a more complicated gene structure, including retrotransposon-like sequences and small segments of chloroplast genome.