QTL Mapping And Candidate Gene Cloning Of Grain Related Traits In Common Wheat(Triticum Aestivum L.)

Wheat is the third largest crop in China.With the growing of population and the reducing of arable land,genetic improvement of wheat yield potential is very important for food security in China.Integrating the genetic improvement with conventional breeding methods will provide an effective approach to boost breeding efficiency,but the prerequisite is to map and clone QTLs/genes for yield or yield related traits.Here,three QTLs/gene for wheat grain weight or shape were identified,among which two were further fine mapped and candidate genes were cloned.The main results obtained are as follows:1.Phenotypic analysis revealed that the TKW of Fu4185 was much higher than that of Shi4185 under five different environments.At the genomic level,110 of 2019(5.4%)simple sequence repeats(SSR)markers showed polymorphism between Shi4185 and Fu4185.Notably,30%(33 out of 110)polymorphic SSR loci were located on the D-genome,which was higher than the percentage of polymorphisms among natural allohexaploid wheat genotypes,indicating that mutations induced by gamma radiation could be a potential resource to enrich the genetic diversity of wheat D-genome.Moreover,one QTL,QTkw.cau-5D,located on chromosome 5DL,with Fu4185 contributing favorable alleles,was detected under different environments,especially under high temperature conditions.In addition,compared with Shi4185,Fu4185 obtained larger general combining ability effect for TKW by 1.68 g.Taken together,these data revealed that mutations induced by gamma radiation could be a potential resource to enrich the genetic diversity of wheat D-genome,and QTkw.cau-5D from Fu4185 may be a desired target for genetic improvement of wheat kernel weight.2.QTL mapping was firstly carried out using H/N recombinant inbred line population,which was derived from two common wheat accessions,Hesheng 2(large kernel,TKW>60 g)and Nongda 4332(small kernel,TKW<30 g).One stable major QTL with pleiotropic effect on plant height(PHT),spike length(SL),spikelet number per spike(SN),TKW and grain length(GL)was detected between marker 3D-SSR7 and 3D-SSR2 on chromosome 3D.Furthermore,comparative genomics study was performed to facilitate marker enrichment for positional cloning.TaWGl-3D was predicted to be a possible candidate gene.Comparing with Hesheng 2,the eighth exon of TaWGl-3D in Nongda 4332 had a single-base substitution mutation,which resulted in an amino acid substitution from glutamate to lysine.The heterogeneous expression of TaWGl-3D in Arabidopsis was performed,and results showed that the transgenic plants with coding sequence from Nongda 4332 were significantly smaller than that of Hesheng 2.In addition,300 hexaploid wheat accessions and 30 Aegilops tauschii accessions were used to check the genotype frequency of TaWG1-3D.Results showed that all of the tested accessions had the same genotype with Hesheng 2,indicating that TaWG1-3D from Nongda 4332 was a rare allele.3.Mapping and map-based cloning of muti-ovary gene in wheat was performed with F2and F2:3 populations,which were derived from Yuan 29(multi-ovary florets)and Chinese Spring(normal florets)Multi-ovary florets of the F1 progeny were observed in reciprocal crosses,indicating that multi-ovary trait was controlled by a dominant nuclear gene.SNP markers linked to multi-ovary gene was firstly identified by 90K iSelect SNP chip with a bulked segregation analysis(BSA)strategy.Based on genome sequences of Aegilops tauschii,marker enrichment for positional cloning was further performed through a comparative genomics approach.Multi-ovary gene was finally mapped into a 3.50 cM interval flanked by 2D-SSR11 and 2D-SSR12,with a gentic distance of 1.19 cM and 2.31 cM,respectively.TaTG2-2D was predicted to be a possible candidate gene.Specific expression of TaTG2-2D was observed in root at the seedling stage and immature inflorescence at the shooting stage with an exception of leaf of Yuan 29,while no expression was detected in none of those three tissues of Chinese Spring,indicating that multi-ovary trait might be originated from a gain-of-function mutation.However,no DNA variation at the 5.0 kb sequence 5’ upstream from the ATG site of TaTG2-2D was found between Yuan 29 and Chinese Spring,suggesting that this expression discrepancy might be triggered by modifications to the epigenetic state of TaTG2-2D.