Dissection And Fine-Mapping Of QTGW1.2a For Thousand Grain Weight In Rice

Grain weight and grain size are typical quantitative traits,which are closely related to the yield and quality of rice.The quantitative trait is mainly controlled by a small number of major effect genes and a large number of minor effect genes.The major effect gene has the characteristics of large additive effect and high heritability and has been the first choice for research.However,the number of major effect genes is limited,so its explaination of the grain weight and grain size genetic mechanism is also very limited.Therefore,it is very important to explore the minor QTL for grain weight and grain size.In the previous study,BC₂F₅,BC₂F₆ and BC₂F₇ populations derived from Zhenshan 97?ZS97?///ZS97/ZS97/Miyang 46?MY46?were used to detect QTL.Two QTLs which controll grain weight and linked each other on the long arm of chromosome 1 were detected,namely,qTGW1.1 and qTGW1.2.Then,the qTGW1.2 was separated into qTGW1.2a,qTGW1.2b and qTGW1.2c by using 6 sets of BC₂F_10:11 near isogenic lines.In this study,qTGW1.2a,which locaed in the RM11730-RM11762 region,was targeted for marker screening and population construction,and then qTGW1.2a was validation,fine mapping and dissection.The main results are as following:1 Validation and Dissection of qTGW1.2aAccording to the preliminary positioning of the 1000-grain weight QTL qTGW1.2a,one BC₂F₁₀plant,which was heterozygous in the Wn33011-Wn33304 interval,was selected from the high-generation group derived from ZS97³/MY46,and the BC₂F₁₁1 population produced by the selfing progenies of the residual heterozygote.By the marker assay,three plants were selected,two plant heterozygous in Wn33011-Wn33252 and one plant heterozygous in Wn33252-Wn33304.In the resultant BC₂F₁₂ populations,non-recombinant homozygotes were identified and selfed to produce homozygous lines.Three NIL populations,namely L1,L2 and L3,were developed and used for QTL analysis.1000-grain weight?TGW?,grain length?GL?and grain width?GW?were measured in the three NIL populations.Genotypic effects were all non-significant on GL but highly significant?P<0.0001?on TGW and GW in two populations,L1 and L2.In addition,the enhancing alleles for TGW and GW in both populations were all derived from MY46,which are in consistent with the effects of qTGW1.2a previously reported.As for the remaining population,L3,genotypic effect was non-significant on TGW but significant on GW.The enhancing allele for GW was derived from ZS97.Apparently,the variation detected in the L3 population was not due to qTGW1.2a.Therefore,two QTLs for grain weight and grain size were included in the region of qTGW1.2a,namely,qTGW1.2a1 and qTGW1.2a2.Comparing the genotype composition of the three populations,qTGW1.2a1 were delimited in an interval flanked by InDel markers Wn32886 and Wn33252,corresponding to a 366.1 kb region in the Nipponbare genome.Following updated information of qTGW1.2a1 location,two BC₂F_14:15 and three BC₂F_16:17 were developed,respectively.qTGW1.2a1 was further fine-maped in an interval flanked by InDel markers Wn33011 and Wn33186,corresponding to a 175.1 kb region in the Nipponbare genome.2 Dissection of qTGW1.2a1 and candidate genes analysis for one of the QTLBased on the above results,five BC₂F₁₆6 plants were screened,and their heterozygous regions cover the entire heterozygous region of qTGW1.2a1,commonly.In the resultant BC₂F₁₇7 populations,non-recombinant homozygotes were identified and selfed to produce homozygous lines.Five BC₂F_17:18populations were developed and used for QTL analysis.1000-grain weight,grain length,grain width and the ratio of length to width?RLW?were measured in the five populations.Comparing the genotype composition of five NIL populations,two QTLs for grain weight and grain size were included in the region of qTGW1.2a1.The first QTL qGL1-33.0 located in a 60.9 kb region of Wn33011-Wn33072maily contributed to grain length,the other QTL qTGW1-33.1 located in a 35.6 kb region of RM212-Wn33089 mainly contributed to grain weight.Interestingly,we also found that the direction of additive for grain length in qGL1-33.0 and qTGW1-33.1 was opposite.When the two QTL co-separation in a target region of qTGW1.2a1,the qTGW1.2a1 show a smaller effect for GL.When the two QTLs were dissected,the effect for GL became larger.Due to hight effect for TGW,qTGW1-33.1 was selected for further analysis.The target segment has five open reading frames.Supporting from transcript sequencing,DNA sequencing and bioinformatics analysis,we speculated that ORF5 might be the target gene for qTGW1-33.1.