MUTATOR-INDUCED MUTATIONS OF THE RF1 NUCLEAR FERTILITY RESTORER OF T-CYTOPLASM MAIZE ALTER THE ACCUMULATION OF T-URF13 MITOCHONDRIAL TRANSCRIPTS

Dominant alleles of the rf1 and rf2 nuclear-encoded fertility restorer genes are necessary for restoration of pollen fertility in T-cytoplas m maize. To further characterize fertility restoration mediated by the Rf1 allele, 123,500 gametes derived from plants carrying the Mutator transposable element family were screened for rf1-mutant alleles (rf1- m) Four heritable rf1-m alleles were recovered from these populations. Three rf1-m alleles were derived from the progenitor allele Rf1-IA153 and one was derived from Rf1-Ky21. Cosegregation analysis revealed 5. 5- and 2.4-kb Mu1-hybridizing EcoRI restriction fragments in all of th e male-sterile and none of the male-fertile plants in families segrega ting for rf1-m3207 and rf1-m3310, respectively. Mitochondrial RNA gel blot analyses indicated that all four rf1-m alleles in male-sterile pl an ts cosegregated with the altered steady-state accumulation of 1.6- and 0.6-kb T-urf13 transcripts, demonstrating that these transcripts a re Rf1 dependent. Plants carrying a leaky mutant, rf1-m7323, revealed variable levels of Rf1-associated, T-urf13 transcripts and the degree of pollen fertility. The ability to obtain rf1-m derivatives from Rf1 indicates that Rf1 alleles produce a functional gene product necessary for the accumulation of specific T-urf13 transcripts in T-cytoplasm m aize.