Toxin resistance and/or male fertility reversion is correlated with defined transcription changes in the 1.5 kb AvaI region of cmsT.

Reversion of T type cytoplasmic male sterility (cmsT) to fertility is correlated with sequence changes in a 1.5 kb AvaI fragment. This 1.5 kb AvaI fragment is composed of 5' flanking sequences of ATPase subunit 6, one complete open reading frame (ORF 13) and part of the another (ORF 25). The sequence of the 1.5 kb AvaI fragment was compared to the sequences of homologous regions in the N (male fertile) and T revertant V3 mitochondrial DNA. Sequences were found to diverge between ORF 13 and ORF 25 coding regions. To further characterize the transcription of these rearranged sequences, specific probes for ORF 13, ORF 25 and 5' flanking sequences of ATPase 6 were hybridized to Northern blots of N, cmsT and the T revertant V3 and V18 mtRNAs. Each revertant has a single ORF 25 homologous transcript in contrast to the multitranscript pattern in cmsT. ORF 13 homologous transcripts were not detected in either revertant cytoplasm. The loss of ORF 13 and/or altered ORF 25 transcription in the fertile revertants may be responsible for the male fertility and/or toxin resistance in these plants.