Submitted to: Plant Molecular Biology International Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 7/31/1997
Publication Date: N/A
Technical Abstract: Cytoplasmic male sterility (CMS) systems are often attributed to chimeric open reading frames in the mitochondrial genome. Transcripts originating from these open reading frames are translated into unique mitochondrial proteins, which often interfere with mitochondrial function and pollen development. Nuclear restorer (Rf) genes function to suppress the effects of CMS-associated mitochondrial abnormalities on male fertility. In some instances they accomplish this by altering the accumulation of CMS- associated mitochondrial transcripts. It has been hypothesized that many of these altered transcripts arose via RNA processing activities mediated by the nuclear restorer genes. We have been characterizing various nuclear restorer genes which mediate CMS-associated, mitochondrial-transcript processing. Rf8 is a newly-described nuclear gene that can substitute for Rf1 to partially restore pollen fertility to male-sterile, T-cytoplasm maize. Although Rf8 is unlinked to the rf1 locus, it also alters T-urf13 mitochondrial transcript accumulation and reduces the accumulation of the URF13 protein. Like the 1.6- and 0.6kb T-urf13 transcripts that accumulate in T-cytoplasm plants carrying Rf1, 1.42- and 0.42-kb T-urf13 transcripts accumulate in plants that are partially restored by Rf8. Another rare, weak restorer factor, Rf*, is uniquely associated with the accumulation of 1.4- and 0.4-kb T-urf13 transcripts. Primer extension analyses positioned the 5' termini of the 1.42/0.42-kb and 1.4/0.4-kb transcripts at +137 and +159 nucleotides, respectively, 3' of the AUG initiation codon of the T- urf13 reading frame. The conserved motif, 5'-CNACNNU-3', overlaps the 5' nucleotides of the Rf1-, Rf8-, and Rf*-associated transcripts.