Analysis Of The Pyramid Effect Of Major Genes In Panicle And Grain Shape Based On Single Segment Substitution Lines In Rice

Rice is one of the most important foods in the world,and half of the world’s population uses rice as the main food source.The yield of rice is mainly composed of panicles number,grains number per panicle and 1000-grain weight,which are usually called the three factors of yield.The panicle traits of rice occupy a certain position in the yield composition.Panicle length is an important factor affecting the number of grains per panicle,and the grain in the upper part of the panicle is usually heavier than the lower part of the panicle,which further affects the 1000-grain weight.Therefore,the cultivation of varieties with a reasonable 1000-grain weight and grains number of per panicle is the prerequisite for high yield.With the development of science and technology,more and more genes related to rice yield and quality have been mapping.In this huge rice germplasm gene bank,the breeders evaluate the gene function under different backgrounds,and use excellent alleles to carry out molecular design and breeding.In this study,a single segment substitution line（SSSL）was used to carry out allelic analysis of genes controlling rice panicle type,and a new allele was identified through marker screening and sequencing.Then,we pyramiding the panicle type gene and the grain shape gene,and analyzed the agronomic traits of the homozygous lines.The main results are as follows:1.Haplotype analysis of panicle type genes.A new panicle type allele dep2 was identified.We used wild rice and HJX74 backcross to obtain a single segment substitution line which carrying dep2 gene.The agronomic traits of NIL-dep2 were significantly different from HJX74.Sequencing analysis shows that there are a large number of single-base mutation sites（SNPs）and amino acid variation sites in wild rice donor parents.These amino acid variations may be located in the functional region of the dep2 protein,causing phenotypic changes.Sampling analysis at the heading stage showed that dep2 was expressed in roots,stems,leaves,leaf sheaths,panicles and spikelets.It was found that the expression of dep2 was highest during the panicles development period,but the expression level was not significantly different from NIL-dep2 and HJX74,we assume that the mutation is mainly caused by sequence differences.Further,the 3 cm young panicles were used for q PCR analysis of rice grain shape genes and BR-related genes,and the expression levels of some grain shape genes and BR-related genes changed.There is no new allelic variation in NIL-dep1,but the grains number of per panicle is significantly higher than that of HJX74,which can be used for pyramid breeding.2.Analysis of the pyramid effect of dep2.Through conventional hybridization and molecular-assisted selection,we obtained 7 pyramided lines of dep2 and different grain size genes,it include gene GS2,GL3.1,GW5,gw8^amol,gw8,GS5,and GLW7.The analysis of the main agronomic traits showed that the 1000-grain weight,plant height,and panicle length of 7 pyramided lines were between NIL-dep2 and HJX74.The grain wide of NIL-dep2/GS2 is the widest,up to 3.43 mm,more than 20%of HJX74,The grain wide of NIL-dep2/GW5 is 3.31 mm;NIL-dep2/gw8^amolhas the most grains number of per panicle,there are 1560 grains per plant in total,26%higher than HJX74,NIL-dep2/gw8 also has1550 grains.The gw8 gene may lead to an increase in the grains number of per panicle.This provides new materials and new ideas for the collaborative improvement of grain shape and panicle type.3.Analysis of the pyramid effect of dep1.Through conventional hybridization and molecular-assisted selection,we obtained 7 pyramided lines of dep1and different grain size genes,it include gene GS2,GL3.1,GW5,gw8^amol,gw8,GS5,and gs3.The agronomic traits of 7 pyramided lines were identified and analyzed.The plant height and panicle length of 7pyramided lines were between NIL-dep1 and HJX74 and the number of grains was higher than NIL-dep1 and HJX74.Among all the combinations,the grain lengths of NIL-dep1/GS2,NIL-dep1/gw8^amoland NIL-dep1/gw8 have increased compared to NIL-dep1,respectively.10.87 mm,8.74 mm and 8.65 mm;the 1000-grain weight of NIL-dep1/GS2 increased significantly,it reached 28.18 g,which was 6%higher than that of HJX74.In this study,a new dep2 allele from wild rice was excavated.The mutant dep2 had a shorter grain length,shorter plant height,and shorter panicle length.A series of dwarf erect materials were obtained by pyramiding the new alleles and grain size genes.It’s provide a good material for the next step of designing plant type breeding and exploring the genetic regulation network of rice grain shape.