Identification Of Quantitative Trait Loci Controlling Kernel Traits And Characterization Of The TaWTG1 In Wheat

Os WTG1(LOC_Os08g42540.1)functions as an important factor determining grain size and shape in rice.Our understanding on its ortholog in wheat,Ta WTG1,is limited.Here,we identified and mapped Ta WTG1 in wheat,characterized its gene and protein structures,predicted transcription factor binding sites of its promoter,and the expression patterns were also analysed based on real-time quantitative PCR and public available microarray data.The WTG1 orthologs in barley(Hv WTG1),rice(Os WTG1),Aegilops tauschii(At WTG1),Triticum urartu(Tu WTG1),Triticum turgidum(Tt WTG1)and Brachypodium distachyon(Bd WTG1)were also identified for comparative analyses.In addition,to identify and characterize quantitative trait loci(QTL)controlling kernel length(KL),kernel width(KW)and thousand-kernel weight(TKW),a recombinant inbred line(RIL)population containing 199 lines was constructed by crossing ‘20828’ and ‘Chuannong 16’(‘CN16’).The Wheat55 K SNP array and SSR markers were used to genotype the RIL population.Further,a kompetitive allele-specific PCR(KASP)marker,KASP-AX-94721936,was developed to narrow the interval based the results of Wheat660 K SNP array on ‘20828’ and ‘Chuannong 16’.KASP-AX-94721936 was integrated into genetic maps based on the results of genotyping in the RIL population.The results of this study are listed as follows:1.Ta WTG1 was mapped onto the short arms of group 7 chromosomes(7AS,7BS,and 7DS).Multiple alignments indicated that WTG1 possesses eight exons and seven introns in all the orthologs,except for the orthologs on 7A of wild emmer and 7D of A.tauschii(seven exons and six introns).An exon–intron junction composed of intron 2 to intron 3 and exon 2 to exon 4 was highly conserved.WTG1 exists a conserved domain(Peptidase_C65).2.WTG1 was mainly expressed in wheat roots,spikes and grains,in barley caryopsis and roots,and in rice anthers.Drought and heat stresses significantly regulated the expression of Ta WTG1 in wheat.Hv WTG1 was significantly down-regulated under Fusarium at late stage.3.A total of 13 QTL conferring kernel traits were detected.Three major QTL(QKL.sicau-2D.1,QKW.sicau-2D and QTKW.sicau-2D)conferring KL,KW and TKW,respectively,were located in the same region on chromosome 2D and detected in different environments.They can separately explain 8.82-20.84 %,6.6-20.13 % and 8.12-19.22 % of the phenotypic variation.Positive alleles of three stable major QTL were derived from ‘CN16’.4.Combining KASP marker,three major QTL were finally co-localized in a region at 0.7 c M flanked by AX-111096297 and KASP-AX-94721936 on the short arm of chromosome 2D.