Positioning the Rf8 and Rf* restorers of fertility loci in the maize genome

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2000
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Pei, Deqing
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Wise, Roger P.
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T-cytoplasm male sterility (cms-T) has been developed as a model system to study the genetic and molecular mechanisms underlying male sterility and fertility restoration. Male sterility in T-cytoplasm maize results from the action of a T-cytoplasm specific, mitochondrial gene, T-urf13. Full (or partial) fertility restoration of T-cytoplasm maize is mediated by one of three (Rf1, Rf8, or Rf*) nuclear restorers, in combination with the Rf2 restorer. Because Rf8 and Rf* are weak fertility restorers and environmentally sensitive, the most robust method to identify plants carrying them is to assay for the accumulation of Rf8- or Rf*-specific, T-urfl3 transcripts via mitochondrial northern hybridization. Therefore, we performed AFLP-bulk segregant analysis on progeny segregating for Rf8 in an attempt to identify a DNA-based marker for this restorer. Sequence analyses of Rf8-finked AFLP fragments facilitated the design of a STS marker, which cosegregates with whp1 on maize chromosome 2L. Additional SSR and RFLP markers flanking this locus were used to more precisely position Rf8 on the maize genetic map. Allelism tests indicate that Rf8 and Rf* were either alleles of one single locus or tightly linked genes. In addition, optimal conditions for establishing a transformation system for functional analysis of cloned genes associated with cms-T were identified. Six additional Rfl-m alleles were also identified from transposon tagged families using improved AIMS approach. These AIMS fragment were tested and shown to be low copy sequence via gel blot analysis. They can be used as probes in physical analysis of rf1 genomic region.
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