Genetic analysis of nuclear control of T-urf13/orf221 transcription in T cytoplasm maize.

The mitochondrial gene T-urf13 in T cytoplasm maize is associated with sensitivity to disease toxins and with cytoplasmic male sterility. T-urf13 is co-transcribed with an open reading frame designated orf221. We have detected alterations in the transcription of the T-urf13/orf221 region that are affected by nuclear genotype. There are multiple mRNA transcripts generated from the T-urf13/orf221 region, one of which is a processed 1538-nucleotide (nt) transcript. This 1538-nt transcript is present in Wf9 (T), but was not found in mitochondrial RNAs (mtRNAs) from maize inbreds B14A (T) and 33-16 (T). For B14A (T) a 1500-nt transcript was detected and for 33-16 (T) a 1400-nt transcript was detected. In F1 progeny of the cross of Wf9 (T) x 33-16 (N), only the 1400-nt transcript was present. Genetic analyses revealed this processing event is nuclear controlled with dominant gene action and is independent of nuclear restorer gene Rf1-associated processing events. T-urf13/orf221 transcriptional patterns were shown to vary in both sterile and fertile states. Segregation analysis of a 1100-nt orf221-specific transcript indicated that the genetic basis of nuclear control for the presence of this transcript was relatively simple. Analysis of the A188 (T4) tissue culture mutant, which has reverted to male fertility but displays the same T-urf13/orf221 transcript pattern as A188 (T), indicated no DNA sequence differences between T4-orf221 and T-orf221. Presence of the nuclear gene Rf2 was not necessary for expression of the T4 cytoplasm-associated malefertile phenotype.