Structural alterations in a transcribed region of the T type cytoplasmic male sterile maize mitochondrial genome.

H. maydis toxin resistance, and cytoplasmic reversion from sterility to fertility in Zea mays T type cytoplasm are correlated with sequence changes in a 6.6 kb XhoI fragment of T mitochondrial DNA. Comparative Northern blot analysis of N (normal male fertile), and cmsT (cytoplasmic male sterile) mitochondrial RNAs using subclones of the 6.6 kb Xho I region of cmsT as probes, reveals different sized transcripts. In cmsT these RNA coding sequences have been mapped onto a 1.5 kb AvaI fragment completely internal to the 6.6 kb XhoI region. Comparative Southern analysis of AvaI digested mitochondrial DNA from cmsT, N and a T-type cytoplasm which has reverted to fertility (designated V3) (Brettel et al. 1979), positions the RNA coding sequences on a 1.5 kb, 2.1 kb and 2.1 kb fragment respectively. These sequence rearrangements in the fertile T revertants create a novel mtRNA transcript. Southern hybridization experiments of other higher plant mitochondrial DNAs using the 1.5 kb Ava I fragment from cmsT mtDNA as a probe, indicate the presence of homologous sequences.