MRG1-1, A DOMINANT ALLELE THAT CONFERS METHOMYL RESISTANCE IN YEAST EXPRESSING THE CYTOPLASMIC MALE-STERILITY T-URF13 GENE FROM MAIZE

We have previously described a eukaryotic heterologous expression syst em, with the urf13TW gene in yeast, which mimics the disease susceptib ility associated with the Texas cytoplasmic male sterility in maize. T his yeast model was used to isolate yeast nuclear mutants conferring m ethomyl resistance. The genetic strategy we have developed focused on screening for nuclear dominant yeast mutations which restore methomyl resistance. MRG1-1, a yeast nuclear dominant allele, was identified as a methomyl-resistance restorer. We have shown that methomyl resistanc e co-segregated with a pleiotropic phenotype in the heterozygous MRG1- 1/MRG1 diploids, detectable even in the absence of the maize-derived m itochondrial protein and/or methomyl. We observed an increase in oxyge n uptake, a significant decrease of the levels of cytochrome aa(3), an d a decrease in the growth yield. This phenotype is influenced by the carbon source and the results suggest a defect in the adaptation to th e respiratory pathway in MRG1-1 yeast cells.