High-density SNP Genetic Map Construction And QTL Mapping For Plant Height And Flowering Time In Brassica Napus

Plant height is an important trait of plant architecture,which is influences seed yield in rapeseed(Brassica napus L.).Flowering is an important process in the life cycle of plants to complete the transition from vegetative to reproductive growth.High-density genetic map using SNPs marker to apply for high accuracy QTL detection and QTL-seq was applied to rapidly detect QTL loci of complex agronomic traits.In this study,a natural variation semi-dwarf mutant(sdw-e)of B.napus was isolated,and two F₂population were constructed from sdw-e with ZS11-HP.Using these two F₂ groups,the main experimental results are as follows:(1)Compared with ZS11-HP,sdw-e has a plant height reduction of about 30%during maturity.In2017,the plant height phenotype of the F₂ population planted in the Wuchang was tested,and the results showed that the plant height distribution conformed to the normal distribution.Fast track approach QTL-seq conducted two extreme DNA bulk derived from F₂ populations in Wuchang 2017 to identify a major region associated with plant height,which suggested QTL interval was 0-12.15 Mb on chromosome A10.(2)The plant height phenotype of 200 individuals of the F₂ population planted in the Yangluo 2018was also identified.The frequency distribution of plant height also conformed to the normal distribution,and the 200 individuals were collected to performed the whole genome re-sequencing.A total of 4323 bin markers were applied to construct high-density genetic map.The genetic map showed total distance2,026.52 c M with an average marker interval of 0.47 c M.Two major QTLs q PHA10.1 and q PHA10.2were identified,accounting for 18.572%and 18.482%of the phenotypic variation for plant height on linkage group A10.In the physical position of the genome,q PHA10.1 and q PHA10.2 are located at2822149bp-8285330bp and 4849685bp-9291804bp,respectively.The q PHA10.1 and q PHA10.2 had a large overlap region.Therefore,we believe that it is a QTL,named QTL-q PHA10,and this result is consistent with the result of QTL-seq.In addition,the apical meristems of the parents were selected for transcriptome analysis.According to the differential expression of the genes and the functional annotation of the Brassica napus reference genome,it was found that there was a significantly differentially expressed candidate gene in the plant height QTL-q PHA10 candidate region.This gene encodes RGA-like protein of the gibberellin signal pathway.Thus,the identified QTL and candidate gene could be used in marker-assisted selection for B.napus breeding in the future.(3)Compared with ZS11-HP,sdw-e has an initial flowering time about a week earlier.The flowering time of 200 individuals of F₂population in Yangluo 2018 were examined,which were in accordance with the normal distribution.Using the constructed high-density genetic map,the QTL at the flowering time was identified,and it was found that there was a major QTL site on the C08 linkage group.The phenotypic variation rate was 13.675%,and it was named QTL-q FTC08.The physical location is between 13654129bp and17847131 bp.According to the genome information of Brassica napus and RNA-seq analysis,two ubiquitination associated genes were predicted candidate genes.