Mapping Of QTL For Grain Shape And Grain Weight In Rice

The genetic research of rice yield-related traits is a hot field of current crop science research.As one of the three elements of rice yield,rice grain weight is mainly determined by grain shape such as grain length and grain width.At the same time,grain shape is also one of the key factors affecting the appearance and processing quality of rice,and it is an important indicator of commercial rice.The small-grain EFT that was an offspring derived from the cross of Chunjiang 06 and TN1 was selected to be crossed with the large-grain FM9 that was an introgression line with Gumei 2 chromosome segments in the Zhongyouzao 81 background,and then an F_2:3 population of 277 individuals and a recombinant inbred line（RIL）population of 211 individuals were obtained.In this study,QTL for rice 1000-grain weight（TGW）,grain length（GL）and grain width（GW）were detected,and the effect of one of the QTLs was validated by using the residual heterozygote-derived segregating populations.At the same time,through scanning electron microscopy observation and q RT-PCR expression analysis of glume epidermal cells,significant changes in the length of spikelet hulls in the direction of grain length,as well as significant difference in the expression of genes related to cell cycle,auxin and grain shape,were observed.The main results are as follows.1.Genetic linkage map construction and QTL mapping of grain shape and grain weight:The genetic linkage map of the F_2:3 population contained 155 pairs of SSR markers and In Del markers spreading over 12 chromosomes with a total length of about 2362.2 c M and an average genetic distance of 15.2 c M.The genetic linkage map of the RIL population contained 170 pairs of SSR markers and In Del markers spreading over 12 chromosomes with a total length of about 1741.8 c M and an average genetic distance of 10.2 c M.29 and 17 QTLs were identified in the two populations respectively,of which 11 QTLs were detected in both populations,18 QTL were only detected in the F_2:3 population,and 6 QTL were only detected in the RIL population,thus a total of 35 QTL for grain shape and grain weight were identified which were distributed on the remaining 10 chromosomes except chromosomes4 and 8.A total of 16 QTLs for GL,13 QTLs for GL and 6 QTLs for GW were detected in the two populations.Among these QTLs,five for TGW,four for GL,and two for GW were shared by two populations and the others were detected in a single population.2.Validation of q TGW1.2/q GL1.2:The effects of the newly identified q TGW1.2/q GL1.2 on TGW and GL were validated by using the segregating populations derived from the two residual heterozygotes RHL17 and RHL124.The additive effects of q TGW1.2/q GL1.2 on TGW and GL are1.11±0.13 g and 0.22±0.01 mm respectively,and the target interval is clearly defined between FIR3596-FIR3892,about 2.96-Mb.3.Scanning electron microscopic observation of epidermal cells of glumes:Scanning electron microscopy was used to compare the number and size of the mature spikelet hulls between the two parent homozygous types q TGW1.2/q GL1.2^FM9and q TGW1.2/q GL1.2^EFT.The results showed that the cells length of spikelet hulls in the grain length direction of long-grained q TGW1.2/q GL1.2^FM9 was significantly increased,but the cell width in the grain width direction was significantly reduced,compared with the short-grained q TGW1.2/q GL1.2^EFT.We speculate that the increase in grain length of q TGW1.2/q GL1.2^FM9 compared to q TGW1.2/q GL1.2^EFT may be caused by the increase in the length of its glume cells.4.Gene expression analysis by q RT-PCR:The expression of 18 cell cycle-related genes,6auxin-related genes and 3 major grain shape genes in the young panicle of q TGW1.2/q GL1.2^FM9and q TGW1.2/q GL1.2^EFT were detected by q RT-PCR.The results showed that 16 related genes showed significant expression changes.Therefore,we speculate that q TGW1.2/q GL1.2 may cause changes in the length of glume cells and grains by regulating cell cycle and cell size.In summary,we used the F_2:3 population and RIL population derived from the same combination to perform primary mapping of QTLs related to rice grain weight and grain shape.By deriving segregating populations,it was validated that the q TGW1.2/q GL1.2^EFT interval located on the long arm of the first chromosome in rice had a significant genetic effect on TGW and GL.The primary mapping of 35 QTLs and the validating of q TGW1.2/q GL1.2 further exhibited the genetic basis underlying grain weight and grain shape of rice,and also laid a foundation for gene cloning and marker assisted selection.