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

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-steri le (cms-T) system was used extensively in the 1960s to eliminate the need f or hand detasseling in hybrid maize production. As a consequence of the 197 0 epidemic of southern corn leaf blight, cms-T is no longer widely used com mercially. However, it has been developed as a model system to study the ge netic and molecular mechanisms underlying male sterility and fertility rest oration. Male sterility in T-cytoplasm maize results from the action of a T -cytoplasm-specific mitochondrial gene, T-urf13. Full (or partial) fertilit y 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 enc odes a protein highly similar to mitochondrial aldehyde dehydrogenases; Rf1 , Rf8, and Rf* each mediate discrete T-urf13 mitochondrial transcript proce ssing events. To test the functionality of Rf1, Rf8, or Rf*, a T-cytoplasm transformation system is under development. AFLP bulk-segregant analysis ha s been used to identify DNA markers closely linked to the Rf8 locus. These tools will provide a foundation for determining mechanisms of nuclear-direc ted mitochondrial RNA processing and fertility restoration.