University of Florida

Mapping the restorer gene Rf3 with RFLPs

--T. L. Kamps and C. D. Chase

Rf3 is the nuclear gene which gametophytically restores fertility to S-type cytoplasmic male sterility (cms-S) of maize. Restoration of male fertility in a gametophytic system is determined by the genotype of the pollen grain. Plants which are heterozygous for Rf3 are semi-sterile (ca. 50% of the pollen grains are aborted). The classical Rf3 gene has previously been mapped to 2L by genetic inversion and translocation experiments (Laughnan and Gabay, MNL 50:45-46). Identification of mapped markers closely linked to Rf3 would more precisely define its position on 2L, facilitate transmission tests of various Rf3 alleles, and be a significant aid in the design of cloning strategies for this gene.

Polymorphism between the male sterile inbred cms-S W182BN/CA and the restored inbred cms-S Ky21 was detected for 2L RFLP markers NPI298, NPI271, NPI456 (Native Plants Inc.), BNL17.14, BNL12.09 (B. Burr, B, Brookhaven National Laboratory), and whp1 (U. Wienand, U, Max-Planck Institut). A BC1 population was generated from the cross cms-S W182BN/CA X (cms-S W182BN/CA X cms-S Ky21). Since only pollen grains with the restoring Rf3 allele can effect fertilization, all progeny from this cross are expected to be semi-sterile (50% pollen abortion). Southern analysis of 47 semi-sterile BC1 plants was used to determine linkage relationships between RFLP marker loci and Rf3. The Rf3 locus mapped between the proximal whp1 and distal BNL17.14 markers. Figure 1 shows the calculated linkage map for all markers tested.

Figure 1. Map of 2L showing genetic position of the Rf3 locus relative to RFLP markers. The recombination percentages (presented as distances in cM) were calculated with data derived from 47 BC1 plants.

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