Fine Mapping Of The Major QTL QHKW3 For Hundred-kernel Weight In Maize (Zea Mays L.)

Maize hundred-kernel weight is one of the important factors affecting yield,which is an important way to improve maize yield by analyzing the genetic mechanism of QTL/gene.CSSLs is considered as an ideal material for identifying QTL and cloning complex yield quantitative traits.In this study,we used a CSSLs as material for cloning the major maize hundred-kernel weight QTL in multi-years and multi-environments,combining with the transcriptome analysis of kernerls at 11 days after pollination（DAP）,7 key candidate genes were obtained in the main effect QTL target region.It laid a good foundation for fine mapping QTLs and screened candidate genes.The main results obtained in this study are as follows:1.Identification of CSSLs that affected maize hundred-kernel weight.By phenotype identification test of H15-6-2 in Baoding,Anyang and Xingtai three environments,the results showed that the average hundred-kernel weight of H15-6-2 decreased about 10g under three environmental conditions and the difference of grain width between Ye478and H15-6-2 was significant（P<0.01）.The grain filling rate of Ye478 was always faster than that of H15-6-2,the results of paraffin section also showed that the grain development of Ye478 was faster than that of H15-6-2.Using the 1021 SSR markers on the maize genome to analyze the imported segments,the results showed that the two imported segments of the control hundred-kernel weight were on the chromosome 3 and6.2.F₂ population construction and hundred-kernel weight QTL mapping.Using H15-6-2 and Ye478 by crossing and selfing to construct a F₂ group and two F_2:3 groups with 207 individuals in 2015 and 2016.Using this group,the main effect QTL of the hundred kernel weight was located in the region about 6Mb between marker C3-89 and C219-90,It is located at 3.08 bin on chromosome 3,accounting for 23%phenotypic variation.The main effect QTL is named qHKW3.3.Fine mapping of qHKW3.12 different types of recombined families was screened in the qHKW3 target region from F_2:3 progenies in Hainan of 2016.According to the genotype and phenotype analysis of these recombination lines,qHKW3 was narrowed in the region about 1.3Mb between marker C214-16 and C215-34.The pure lines of 12recombinant families were planted in two environments（Huanggang and Sichuan）,identifying in the qHKW3 target region of C214-16-C215-34 by progeny test in 2017,which was consistent with the previous fine mapping results.4.Transcriptome analysis of target region.Extracting the RNA of kernel 11DAP of the Ye478 and H15-6-2 for sequencing analysis in the summer of 2017.There are 23candidate genes in 1.3Mb region according to B73 Ref Gen-V4 and RNA-seq.Then detecting seven candidate genes by RNA-seq of Ye478 and H15-6-2 according to the expression difference more than 2 times,therefore as candidate genes.