Fining Mapping Of Fertility Restoration Gene,Rf3 For CMS-S In Maize

Maize is not only an important cereal and energy crop, but also a model plant for the research on genetics and nuclear-cytoplasm i c interaction. Maize is one of the plants being applied the CMS/Rf system into hybrid production. The CMS/Rf system facilitates hybrids producing by reducing the cost of artificial emasculation. Maize CMS-S is the largest group in the three main CMS groups, but its unstable fertility restoration limits its application in hybrid production. Thus it is essential to clone the main fertility restoration gene, R/3, and to clarify its interaction with the sterile gene of CMS-S. Although studies on mapping Rf3 have been carried out, the region is still too large to clone the gene at present. In this study, we expect to fine map R/3 with two BC1 populations derived from a cross of two near-isogenic lines and a cross bewteen S-Mo17Rf3Rf3 and N-B73rf3rf3 by DNA markers designed against the genomic sequence in the region harboring Rf3. Putative candidate genes for Rf3 were also predicted according to the result of fining mapping. Main results of this study are as follows:1, Pollen fertility in the BC1 population of S-Mo17Rf3Rf3/N-Mo17rf3//N-Mo17rf3rf3 was investigated,472 and 445 individuals were scored as sterility and semi-fertility, respectively. After tested by χ2(P=0.41), the segregation ratio fits to 1:1, suggesting that fertility restoration was conditioned by one dominant restorer gene, Rf3, in this population. Seven molecular markers of 44 new designed markers were screened to be polymorphic between S-Mo17Rf3Rf3 and N-Mo17rf3rf3 Two markers, Red2 and 2042S-3, were closest to Rf3, the genetic distance was 3.3cM and 1.6cM from Rf3. However, the two markers were on the same side of Rf3;2, In the BC1 population of S-Mo17Rf3RF3/S-B73rf3rf3//S-B73rf3rf3,285 recombinants were selected from more than 14000 seeds using two flanking markers, Red2 and UMC1256, with the DNA templates extracted from emdosperms of the seeds. In addition, 91 recombinants were screened out from 2875 seedlings of this population with the markers of Red2 and IDP3931 flanked to Rf3. A total of 10 polymorphic markers screened from 248 designed markers were employed to fine map Rf3, and it was mapped between the marker 1839S-18 and Red2 with a physic distance of 1.44Mbp;3. In the MaizeGDB database, the sequence in the region between Red2 and 1839S-18 was retrieved and used to predict candidate genes. In addition some Pentatricopeptide repeats were found. Fertility restorers in other cytoplasmic male sterility plants belong to PPR family, so these PPRs might mostly be candidates of Rf3.