Mapping And Genetic Analysis Of Heterotic Loci In Three Maize Hybrid Populations

Heterosis is a common genetic phenomenon.Studying the mechanism of heterosis can significantly accelerate the breeding process in maize.However,due to population type,size and limited molecular marker density,previous studies on maize heterosis usually constructed a genetic map with lower resolution,identified QTLs in a wider range interval,and identified the positions of heterotic sites with less accuracy.Thus,the important heterotic sites and major candidate genes cannot be well identified across the genome.In this study,three representative maize hybrid combinations,Zheng58×Chang7-2,B73×Mo17 and C428×C434,were used as research materials to construct F₂ generation heterotic populations with total 5360 lines.Low-abundance sequencing of the whole genome was performed on each individual plant using whole-genome sequencing to obtain SNP locus with high polymorphism,and a high-density genetic linkage map was constructed.Meanwhile,phenotypic identification was performed on the parents,F₁ and F₂ of three sets of heterotic populations,and phenotypic data of 19 agronomic traits related to heterosis were investigated.The QTLs controlling phenotypic traits were identified using composite interval-mapping.A total of 628 key QTLs were found in the three sets of heterotic populations?three sets of populations identified 256,214 and 158 QTLs,respectively?.Combining genomic data and phenotypic data to analyze the genetic effects of QTL locus,we found that most loci showed complete-incomplete dominance effects,followed by overdominance effects.Further analyses revealed that the proportion of favorable heterosis alleles from the parents was equal,accounting for about 50%.Among 628 heterotic key QTLs,we selected 17 major effect QTLs that were closely related to heterosis formation.In order to verify whether random errors had an effect on the genetic effect estimates of major loci,we conducted a repeated experiment in the experimental base of Northeast Agricultural University with different environmental conditions.A total of 2225 F₂individual plants of Zheng58×Chang7-2 population were selected for phenotypic statistics and analysis of agronomic traits.By comparison,the genetic effects of the heterotic main QTL locus obtained under two different environmental conditions were generally consistent and stable.We selected one of the major QTL loci KY4q19 for in-depth analysis,and found that a known maize gene ub3 exists in the loci.This gene regulates the number of male tassel branches and maize yield and is homologous to the rice heterosis gene IPA1.By comparing the gene sequences of the parent to the hybrid,it was found that there are no differences in the coding region of the ub3 but differences in the promoter region.These differences are likely to cause the differential expression of the gene between the parents and offspring.These results indicate that there may be a number of common functional genes and different regulatory nodes between maize parents and hybrids,which together determine the heterosis in the crop,and provide new ideas for maize hybrid breeding.