Fine Mapping QTL For LP And SI On Chromosome 21 In Cotton(Gossypium Hirsutum L.)

Cotton is the most important natural fiber crop in the world.China is both the world’s largest producer and consumer of raw cottons.Cotton fiber,the primary product of cotton,is an indispensable and important material for the textile industry,and cotton seeds,a coproduct of cotton,is also a significant source of protein,edible oil and biofuel.Cotton fiber differentiated from ovule epidermal cells,which determines the inevitable competition between cotton seeds and fiber for photosynthetic products during development.Conventional breeding for cotton fiber yield improvement is often based on the sacrifice of seed yield,and the high yiled cultivar offten has smaller seeds which in turn limits the increase of cotton fiber yield.Therefore,through molecular marker-assisted selection breeding technology to ensure good seed development and to increase the yield potential of cotton,achieving synergistic improvement of fibre and seed is important to make steady progress toward the high quality development of China’s cotton industry.In this study,the introgression line CSSL＿333 from G.tomentosum P0601211introgression population with the background of G.hirsutum CCRI35,was crossed to CCRI35 to develop F₂ and F_2:3 populations,the QTL for lint percentage and seed index on chromosome 21 was fine mapped,and the QTL candidate genes were identified.The main findings are as follows.1.Genetic linkage map of QTL regionBased the reference genome sequences of G.hirsutum and G.tomentosum,156InDel marker primers were designed and tested for polymorphism between parent CCRI35 and CSSL＿333,and 44 polymophic primer were obtained.The genotype of three SSR and 44 InDel from F₂ population were constructed genetic map.The QTL region map contained three SSR and 44 InDel markers,covering 90.5 c M with an average genetic distance of 1.93 c M between markers.QTL region physical maps were constructed based on the physical location of the SSR and InDel markers on the reference genome of G.hirsutum and G.tomentosum,respectively.When the linear relationships between the physical maps of QTL region and the genetic map were compared,it was discovered that these markers had identical linear relationships between the three maps,indicating that the constructed genetic linkage map of QTL region are accurate.2.Fine mapping of lint percentage and seed index QTL on chromosome 21Based on the QTL region map and,the lint percentage and seed index tested from2030 individuals in F₂ population and 5369 individuals in F_2:3 population,the lint percentage QTL（q LP21.1）and seed index QTL（q SI21.1）were mapped between marker D11＿10.01 and D11＿10.263 on chromosome 21.For q LP21.1,the LOD value was 28.14,the additive effect was 1.3 and the explained phenotypic variation is 8.2%.For q SI21.1,the LOD was 36.08,and the additive effect was-0.43,and the explained phenotypic variation was 10.4%.The q LP21.1 favorable allele was derived from G.tomentosum（P0601211）,and the q SI21.1 favorable allele was derived from G.hirsutum（CCRI35）.3.Candidate genes of q LP21.1 and q SI21.1The QTL region responded 253 kb in G.hirsutum reference genome and contained twenty-two annotated genes.Based on q RT-PCR analysis of annotated genes in CSSL＿333 and CCRI35 ovule,and the transcriptome sequencing data of CCRI35,six genes（Gh＿D11G1092、Gh＿D11G1095、Gh＿D11G1104、Gh＿D11G1107、Gh＿D11G1108、Gh＿D11G1110）was identified as candidate genes of q LP21.1 and q SI21.1.