Plant & Animal Genomes XI Conference Plant & Animal Genomes XI ConferenceJanuary 11-15, 2003
Town & Country Convention Center
San Diego, CA
Poster: Maize, Sorghum, Millet, Sugarcane, and related
Ten percent of the eukaryotic nuclear genome is dedicated to mitochondrial biogenesis and function. Because genetic mutations disrupting mitochondrial respiration are lethal in higher eukaryotes, forward genetic analysis of mitochondrial function has been restricted to facultative anaerobes. This problem is circumvented by the S system of cytoplasmic male sterility (CMS-S) in maize. Expression of a mitochondrial CMS-S gene results in the collapse of developing pollen, but restorer-of-fertility (Rf) alleles that disrupt pollen mitochondrial gene expression are recovered by spontaneous mutation at many different nuclear loci. Rf mutations are observed as sectors of male fertility on male-sterile tassels and recovered by crosses with the fertile pollen. These mutations are readily observed because pollen is a haploid, fermentative tissue. Introduction of Ac-Ds or En-Spm transposons into CMS-S maize increased the frequency of Rf mutations ten-fold over background. We recovered 12 new Rf mutations from a screen of 1,241 Ac-Ds plants, and 27 new Rf mutations from a screen of 1,235 En-Spm plants. Seventeen Rf mutations were selected for further study. Five of these are homozygous lethal due to failed seed development. Instability of the mutant lines, evidenced by high-frequency reversion and second site mutation, necessitated backcrossing into a stabilizing inbred background prior to molecular-genetic studies. Chromosome mapping of Rf mutants by means of waxy-marked translocations is now in progress. Thermal asymmetric interlaced (TAIL) PCR protocols were developed and used to screen for both standard Ds and Ds1 elements co-segregating with Rf alleles recovered from the Ac-Ds populations.