Study On Maize Flowering Time Regulation Of Mixed Selection Population Model Combined With Multiple Pathways

Maize（Zea mays L.）was native to the tropical region and its wild ancestor is teosinte.After a long period of artificial domestication and improvement,maize has become a widely cultivated crop in the world,it is planted in the range of 50°N to 45°S.Because tropical maize has higher genetic diversity and shows a series of excellent agronomic traits,thus it can be used in the mazie germplasm resource improvement.However,the photoperiod sensitivity of tropical maize is higher,and if it was direct planted in the tropical region,it would cause inconsistent with growth period.Thus it is necessary to perform the adaptive improvement of tropical maize.Flowering time is one of the significant agronomic traits in maize adaptive improvement process,which controls the transition of growth cycle.Thus it is important to reveal the maize genetic mechanism and discover flowering time genes.One of the enormous challenges in understanding the genetic regulation pathway is that flowering time is a quantitative trait,which is greatly influenced by population structure.Our research chose the original improvement population Pop32C0 and the different circles improvement population C3 and C5,which obtained by mixed selection method.Each population was used to perform the bulked sample analysis,we obtained high quality SNPs markers.By combing theΔSNP index calculation and WGCNA methods,we identified a number of flowering time candidate genes.The F_ST and XP-EHH signal were calculated by using the genotype data which extracted from the maize Hapmap3,and a series of flowering time genes were screened out.In this study,the association analysis were used to identify the correlation degree between candidate flowering time genes and flowering traits,and further validated the biological function of candidate flowering times genes by qRT-PCR.The main experimental conclusions are as follows:1.The original improvement population of the tropical maize Pop32,and the improvement population in different cycles C3 and C5 were selected,and then the three maize populations were planted in the temperate region Beijing to record the flowering time days.The results discovered that the flowering time days were 91.6 days in C0 generations,and reduced to 84.4 days in C3 generations,and eventually reduced to 78.4 days in C5 generations,the C5 generations could normally pollination,silk and fructification.The field trial revealed that bi-parental mass selection method could effectively improve the agronomic traits of tropical maize,making the tropical maize adapting to the temperate region and accelerating the breeding process.2.The adaptive improvement generations C0,C3,C5 of pop32 were selected to perform the bulked sample analysis.We finally get 4973810 high quality SNPs through SNP calling process.By calculating theΔSNP index value,we finally obtained 6517 candidate genes.Gene function annotation had discovered several genes which participate in the flowering time regulation pathways,for example,GRMZM2G019879,GRMZM2G171365.3.Analysising the gene expression of different tissues.5242 high expression level genes were screened out from the candidate gene set,and used to construct the WGCNA.And 13 tissue specific modules were obtained with strong biological significance.The GO annotation of tissue specific module genes showed that the Blue,Cyan,Darkturquoise and Black module all could obtain flowering time development and regulation GO terms.And several flowering time genes which had reported in the literature were discovered,including GIZG1A,ZmMADS3,ZmMADS1,ZMHD6,ZFL1 etc.We had filtered out the genes which highly connected to the flowering time genes,and construct the flowering time genes regulation network,and identified a series of flowering time genes.4.557 and 1913 candidate genes were identified by using the F_STT and XP-EHH methods,respectively.Several flowering time genes were identified from the candidate gene set,including ZmCCT9,COL1,GRMZM2G387528.5.In this study,the genes identified through above analysis were analyzed by candidate genes association analysis which related to the flowering time trait,and the result showed that the proportions of phenotypic variance of candidate genes were higher than the flowering time genes,for example,GRMZM2G317900,GRMZM2G019879,GRMZM2G126506.TheGRMZM2G019879,GRMZM2G058158,GRMZM2G171365,GRMZM2G055905 were selected to perform the qRT-PCR,the results discovered this candidate flowering time genes were significantly differential expression in different maize development tissues.It can be used to explore the biological function in the following experiments.