Mapping And Study Of Genetic Mechanism Of Segregation Distortion Loci On Rice

Indica and japonica are two subspecies of Asian cultivated rice.Currently,intraspecific hybridization is widely used for hybrid rice breeding,and grain yield of the intraspecific hybrids has stagnated.Inter-subspecific heterosis is an effective way to increase the yield potantial.Because of the reproductive isolation between the subspecies,the subspecific hybrid offspring will appear hybrid incompatibility and semi-sterility,which hinders the use of inter-subspecies heterosis.Segregation distortion,an important driving force in the evolution of species,is a common phenomenon of the reproductive isolation.The study of segregation distortion is helpful to understand the mechanism of the reproductive isolation,and provides a theoretical foundation for crop genetic improvement and for utilization of inter-subspecies heterosis.To aim at revealing the genetic causes of segregation distortion and providing a practical basis for molecular mechanism of segregation distortion,the present study used the chromosome segment substitution lines and recombinant inbred lines that were derived from a japonica variety Nipponbare as donor parent,and the indica variety ZS97B and 9311 for recipient parent respectively,to detect segregation distortion loci and its genetic effect.The main results are as follows:1.Using the F2 population from the cross between ZS97B and XJ91,a chromosome segment substitution line carrying a target NIP segment with the genetic background of ZS97B,we have detected two segregation distortion loci,HW1 and HW2 on chromosome 4.The offspring genotypes at each of the two heterozygous loci were biased towards ZS97B genotype.2.The nine genotypes at HW1 and HW2 in the F2 poupation are all pollen fertile.Analysison frequencies of the nine genotypes,showed that the gametes selection not the zygotes selection is responsible for the distorted segregation at the two loci.3.Analyzing the two loci interaction in the F2 population,we found that HW1 appears segregation distortion when HW2 is ZS homozygous or NIP/ZS heterozygous,and HW2 distorted when HW1 is NIP homozygous or NIP/ZS heterozygous.4.We developed a RIL population that derived from NIP and 9311,and constructed a genetic linkage map using 185 molecular markers.Of them 82 markers(44.32%)showed segregation distortion(P<0.01),56 markers of which skewed toward 9311 genotype and 26 markers skewed toward NIP genotype.The interaction between HW1 and HW2 was also validated in the RIL population.The HW2 may serve as the protector that affects the segregation distortion of other locion the genome.5.We made the reciprocal crosses between the NILs carring the heterozygote NIP/ZS and the homozygote MH/MH respectively at the HW1 locus with the identical genetic background of ZS97B.The reciprocal cross test demonstrated that the segregation distortion of the HW1 locus was due to the adverse selection of the male gametes of NIP,resulted in reduction of the NIP genotype in the offspring.6.By using a large F2 population from the cross between XJ91 and ZS,the HW1 and HW2 loci were mapped into about 600Kb and 1.5 Mb region respectively.