Genetics, Vol 136, 1171-1185, Copyright © 1994

INVESTIGATIONS

Recovery of Heritable, Transposon-Induced, Mutant Alleles of the rf2 Nuclear Restorer of T-Cytoplasm Maize

P. S. Schnable and R. P. Wise
Departments of Agronomy and Zoology and Genetics, Iowa State University, Ames, Iowa 50011

T (Texas) cytoplasm is associated with a mitochondrial disruption that is phenotypically expressed during microsporogenesis resulting in male sterility. Restoration of pollen fertility in T-cytoplasm maize is controlled by dominant alleles at two unlinked, complementary, nuclear-encoded genes, rf1 and rf2. As a first step in the molecular isolation of the rf2 gene, 178,300 gametes derived from plants that carried the Mutator, Cy or Spm transposon families were screened for rf2 mutant alleles (rf2-m) via their inability to restore pollen fertility to T-cytoplasm male-sterile maize. Seven heritable rf2-m alleles were recovered from these transposon populations. Pedigrees and restriction fragment length polymorphism (RFLP)-based analyses indicated that all seven rf2-m alleles were derived independently. The ability to obtain rf2-m derivatives from Rf2 suggests that Rf2 alleles produce a functional product necessary to restore pollen fertility to cmsT. Molecular markers flanking the rf1 and rf2 loci were used to decipher segregation patterns in progenies segregating for the rf2-m alleles. These analyses provided preliminary evidence of a weak, third restorer gene of cmsT that can substitute for Rf1.

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