Mitochondrial transcript processing and restoration of male fertility in T-cytoplasm maize

Abstract

Cytoplasmic male sterility (CMS) systems have been useful in the production of hybrid seed in a number of crops. The Texas or T-cytoplasmic male-sterile (cms-T) system was used extensively in the 1960s to eliminate the need for hand detasseling in hybrid maize production. As a consequence of the 1970 epidemic of southern corn leaf blight, cms-T is no longer widely used commercially. However, it has been developed as a model system to study the genetic and molecular mechanisms underlying male sterility and fertility restoration. Male sterility in T-cytoplasm maize results from the action of a T-cytoplasm-specific mitochondrial gene, T-urf13. Full (or partial) fertility restoration of T-cytoplasm maize is mediated by the Rf2 nuclear restorer in combination with one of three other restorers: Rf1, Rf8, or Rf*. Rf2 encodes a protein highly similar to mitochondrial aldehyde dehydrogenases; Rf1, Rf8, and Rf* each mediate discrete T-urf13 mitochondrial transcript processing events. To test the functionality of Rf1, Rf8, or Rf*, a T-cytoplasm transformation system is under development. AFLP bulk-segregant analysis has been used to identify DNA markers closely linked to the Rf8 locus. These tools will provide a foundation for determining mechanisms of nuclear-directed mitochondrial RNA processing and fertility restoration.

Interactions of Mitochondrial and Nuclear Genes That Affect Male Gametophyte Development

“…Processing events in the presence of each of the restorers occur in different locations within urf13 RNAs; interestingly, the processing sites exhibit some sequence conservation. What remains puzzling, however, is that although the processing events produce transcripts from which URF13 cannot be translated, the restored lines still contain larger transcripts that could encode URF13, with no obvious decrease in RNA abundance relative to CMS lines (Wise et al, 1999). A similar puzzling result has been seen in restored petunia lines, which contain transcripts that could encode the pcf gene product (PCF), even though transcripts with 59 termini -121 to the start codon are decreased in abundance (Pruitt and Hanson, 1991a).…”

Genomic Conflicts that Cause Pollen Mortality and Raise Reproductive Barriers inArabidopsis thaliana

“…The presence of different sets of Rf genes in related genotypes has been reported in other species. For example, in maize, three restorers, Rf1, Rf8, or Rf*, are able to restore fertility, in combination with Rf2 (Wise et al 1999). In radish, Ogura CMS was first described to be controlled by a unique gene in some Japanese radish cultivars (Ogura 1968), but then found to rely on two or three major restoration loci, along with minor ones, in populations from United States or European germplasms (Nieuwhof 1990;Bett 2004).…”

Computational Finishing of Large Sequence Contigs Reveals Interspersed Nested Repeats and Gene Islands in the rf1-Associated Region of Maize

“…Six tightly linked and cosegregating low-copy amplification of insertion mutagenized sites (AIMS) fragments (Frey et al, 1998) were identified from three rf1-m families (Wise et al, 1996) and, along with sequences selected from the cosegregating 6140-1 cDNA (Wise et al, 1999), were used as probes against the first B73 library filters (ZMMBBa; Clemson University Genomics Institute). From each of the resulting short nonoverlapping contigs, overgo probes were designed off sequenced BAC ends.…”

“…A 5.5-kb Mu1-hybridizing EcoRI restriction fragment was identified that cosegregated with the rf1-m3207 allele. Sequences from this fragment were hybridized to a Rf1 cDNA library, and probes designed from the identified cDNA, p6140-1 (Wise et al, 1999), were found to cosegregate with the rf1 locus in a recombinant population selected from over 10,000 progeny.…”