Gene Mapping And Genetic Analysis Of An Early Heading Mutant Eh1 In Wheat

Heading time plays a pivotal role in adaptability to different ecotypes and environmental conditions in wheat?Triticum aestivum L.?,which is one of the important target traits for breeding with high yield stability.The heading time of wheat is mainly controlled by vernalization genes and photoperiod genes.Allelic variations in these two kinds of genes are genetic basis for wide adaptability of wheat.In this study,we used BSA and QTL mapping to identify the related quantitative trait loci and elucidated the genetic mechanism of the early heading mutant eh1.The main results are as follows:1.Based on the RIL population that constructed by crossing the mutant eh1 with Lunxuan987,a stable QTL was detected on chromosome 5B by BSR-Seq and QTL mapping.Further molecular markers were developed to delimit the QTL to 3.31 cM.A large deletion within the first intron of vernalization gene VRN-B1 was identified both in eh1 and wild type by developing new diagnostic markers.Phenotypic analysis with plants carrying different alleles showed that this QTL was caused by the deletion of the large fragment in VRN-B1 and the variation of the VRN-B1 gene was due to the difference of genetic background between eh1 and LX987 parent lines.Comparison of VRN-B1sequences further confirmed the 6850 bp deletion within the first intron of VRN-B1 gene in eh1 and wild type.In addition,gene sequencing showed that there was a 37 bp deletion mutation in the VRN-B1gene in eh1,which was co-segregated with the 6850 bp deletion in the recombinant inbred lines.Further analysis of the F₂ population constructed by eh1 and wild type showed that there was no significant correlation between the 37 bp deletion mutation and heading time.2.BSA based on 660K SNP array identified a locus on chromosome 2A affecting the heading time in the recombinant inbred population.Further analysis by QTL mapping verified the QTL and mapped it to 138.16-141.49 Mb.The sequence analysis of the photoperiod gene Ppd-A1 on chromosome 2A showed that there was no variations between the mutant eh1 and Lunxuan987 lines.In addition,a 131bp mutation occurred downstream of the Ppd-A1 gene in the eh1,which had no significant effect on the heading time in the recombinant inbred population.3.Using the F₂ population constructed by the mutant eh1 and wild-type Zhongyuan 9,two loci were detected on the chromosome 2D and 7D by BSA based on exome-capturing sequencing and QTL mapping.QTL mapping was carried out by developing molecular markers on chromosome 7D to locate the loucs within the range of 3.47 cM,corresponding to 2.54 Mb physical intervel of the reference genome.The results of exome-capturing sequencing showed that the vernalization gene VRN-D3 in the candidate region had a single base mutation between the mutant eh1 and the wild type.Further sequencing confirmed the insertion of C base in eh1.Phenotypic analysis showed that plants with eh1allele heading 7.89 days earlier than plants with wild type allele on average.According to the results of BSA and the identification of VRN-D3 gene,it is inferred that there is another locus affecting the heading time in F₂ population.Further QTL mapping on chromosome 2D confirmed the existence of this QTL and named it Qhd.caas.2D.This QTL was located in a range of 3.94 cM by developing high-density molecular markers.Two way ANOVA analysis showed that VRN-D3 had epistatic effect with Qhd.caas.2D in F₂ population.In this study,QTL affecting heading time of wheat were detected on several chromosomes by using eh1 as the main material.Through the development of diagnostic markers,it was identified that the QTL on chromosome 5B was caused by the variation of vernalization gene VRN-B1,and the effect of the variation on heading time was discussed.Meanwhile,a single base mutation in vernalization gene VRN-D3 on chromosome 7D was identified for leading to early heading of wheat.Identification of these vernalization genes will further deepen the understanding of the genetic mechanism of wheat heading.The identification of loci related to heading time of wheat provides basis for map-based cloning of the related genes,and also offers a theoretical basis for development of novel wheat varieties adapted to different ecological environments.