| Rice black-streaked dwarf disease, caused by rice black-streaked dwarf virus (RBSDV), can lead to severe yield losses in rice. Deployment of resistant cultivars is an effective way to control the disease. At present, genetics and breeding of RBSDV resistance have been reported, but the number and in-depth of such researches is still lacking, which limited the breeding of rice varieties resistant to black stripe dwarf disease. In addition, mimic mutants are useful to studying resitant mechanism, and analysis of target genes conferring the phenotype of mimic mutants can help to elucidate the mechanism of rice disease resistance, promote rice breeding work. Since 2009, we screened the rice varieties and germplasms with resistance to RBSDV, and a RIL population consisting of 208 lines were constructed for resistantce-QTL mapping. Also, the physiological and biochemical analysis of rice lesion mimic mutant has been carried out, and the target gene has been mapped. The main results are as follows:(1) A total of 1026 accessions of rice varieties and germplasms were evaluated to determine their resistance against RBSDV and RSV. Of these rice materials, IR36 and Miyang23, showing no infection of RBSDV and RSV, and L5494 and Wuyujing3, showing highly susceptible to RBSDV (field RBSDV incidences of 66.70% and 58.80%) but resistant to RSV, were selected to cross for developing RIL population.(2) In 2013 and 2014, we planted three RILs in Yandu and Donghai Jiangsu Province. According to the incidence, we choose a RIL population consisting of 208 lines which were developed from the cross between IR36 and L5494 for Construction of genetic linkage map resistantce QTL mapping subsequently. In 2013,the RBSDV incidence of susceptible-parent and Resistance-parent were 28.77% and 5.02%, and the RBSDV incidence showed a continuous distribution from 0 to 38.30% at the location of Donghai. In 2014 Yandu, the RBSDV incidence ranged from 0 to 43.8% and the parents incidence were 20.69% and 5.0%. In 2015, we only identified the incidence of L5494/IR36 population and its parents in Kaifeng. Results indicated that the RBSDV incidences of the parents were 50.93% and 24.32% and the disease incidences of RILs were ranged from 7.49%-88.89%.Out of 640 markers examined,136 markers were found to be polymorphic between the two parents. These markers were analyzed in population. At the end,17 polymorphic markers on chromosome 3 were all significantly deviated from the expected 1:1 or 1:2:1 segregation ratio (P< 0.05) in RIL population, and most lines showed the genotypes of IR36 at these loci. Therefore, A molecular linkage map was constructed that only included 11 linkage groups and covered 2179.6 cM in rice genome was acquired by these markers analysis with an average interval size of 17.16 cM.(4) A total of 12 QTL on chromosomes 1,6,8 and 9 associated with resistance to RSDV were detected in the three seasonal environments (2013-2015).The resistant alleles underlying the QTLs on chromosome 6 and 8 were from the resistant parent IR36, and the resistant alleles underlying the QTLs on chromosomes 1 and 9 were from the susceptible parent L5494. The QTLs in two marker intervals, namely, RM19234-CHR6-2, and RM3700-RM160 on chromosomes 6 and 9 were able to be detected in the three seasonal environments, their contributions to the total variation were ranged from 8.59% to 29.00% and 20.20% to 18.68%, indicating that they are major RBSDV-resistant QTLs, which are useful resources for efficiently breeding resistant rice cultivars to RBSDV.(5) A lesion mimic mutant wy3 was obtained from the progeny of a japonica variety Wuyujing3 by natural mutation. The lesions were first observed on the leaves at the seedling stage, and spreading gradually to the whole leaf at the initial tillering stage. Compared with the wild type, the plant height, the number of effective tiller, panicle length, grain number per panicle and seed setting rate of wy3 were reduced significantly. The shading assay showed that the lesions on leaves of wy3 were induced by natural light. Trypan blue staining experiments showed that the mutant lesion department has a large number of dead cells. Compared with the wild type, the photosynthetic pigment and the net photosynthetic rate of wy3 were significantly reduced, but the SOD activity, POD activity, CAT activity and MDA content of wy3 were significantly higher than that of WT.(6) Genetic analysis suggested that the phenotype of wy3 was controlled by a single recessive nuclear locus, and the target gene was mapped between markers W2-17 and W2-18 with the physical distance of 28 kb on chromosome 2 using F2 populations with 1099 lesion mimic mutant plants. Sequence analysis revealed that the mutated gene in wy3 had a single nucleotide deletion at the 375th in CDS of LOC_Os02g02000, resulting in a premature termination of translation of the target gene, which is an new allele of OsHPL3. |
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