Phenotypic And Genetic Analysis Of Glucosinolates In New-type Brassica Napus

Glucosinolates(GSLs)are secondary metabolites which mainly exist in Brassicaceae plants and play an important role in plant defense.Rapeseed(Brassica napus)is the most prevalent oil crop in genus Brassica of which seed and meal quality are tightly associated with GSLs.In agricultural production,it is an important direction to improve rapeseed quality via reducing GSL content harmful to human or livetock.Enhancing beneficial GSL content would provide new insights for future rapeseed quality improvement.Our lab used to construct a new-type B.napus germplasm pool which possesses abundant exogenous genomic fragments via large-scale interspecies hybridization between Brassica carinata and Brassica rapa.In this study,we first measured leaf and seed GSL content of 240 materials by high performance liquid chromatography(HPLC)which were randomly selected from early generations of the new-type B.napus recurrent selection population.Leaf and seed GSL distribution as well as exogenously introgressed beneficial GSL content were carefully studied.Then we performed whole-genome resequencing and near-infrared spectrum(NIRS)analysis for seed GSL trait among 209 inbred/double haploid accessions from the new-type B.napus genome-wide association study(GWAS)population.Seed GSL profiles were analyzed and genetic analysis was performed by GWAS.Main results were as follows:1)Overall,10 GSLs were detected in new-type B.napus recurrent selection population materials.Among 8 GSLs detected in leaves,progoitrin,gluconapin,glucobrassicanipin and gluconasturtiin are the most abundant GSLs.Among 10 GSLs detected in seeds,progoitrin and gluconapin are the most abundant GSLs while 4-methoxyglucobrassicin and neoglucobrassicin were not detected in leaves.Notebly,we also detected exogenously introgressed and beneficial sinigrin,which is hard to be detected in normal B.napus.2)We performed inner-organ GSL correlation analysis of the new-type B.napus recurrent selection population materials.Except for gluconasturtiin,major GSLs in leaves and seeds all showed strong positive correlations with total GSLs and positive correlations among major GSLs exhibited organ-specific distribution.Further interorgan GSL correlation analysis indicated that progoitrin,glucobrassicanipin,gluconapoleiferin and glucobrassicin showd significant correlations between leaves and seeds.However,there is no significant correlation between leaf and seed total GSL content.3)NIRS results of the new-type B.napus GWAS population indicated that the mean GSL content is at a low level and significant differences of seed GSL content between two Wuhan environments were observed.Significance test showed that genotype is the dominant factor which affects seed GSL trait while environmental factors can also lead to significant change of seed GSL content,especially for high-GSL materials in the new-type B.napus GWAS population.4)We performed GWAS for seed GSL trait of the new-type B.napus GWAS population.Based on GWAS of whole-genome resequencing data and two environments as well as best linear unbiased estimate phenotype values,14 reliable significant regions were detected among 8 chromosomes.We identified 14 seed GSL-related candidate genes in 9 out of 14 flanking regions.Among these candidate regions,9 genes encode transcription factors and 3 genes encode enzymes involved in GSL biosynthesis.Other2 genes encode enzymes responsible for camalexin biosynthesis which shares a same synthetic node with GSLs.Furthermore,we performed LD decay and haplotype analysis for 5 significant regions which didn’t contain identified candidate genes.We confirmed 5 related candidate regions ranging from 3.21 kb to 198.80 kb.This study provided us a systematic understanding of the distribution and diversity of GSLs in new-type B.napus.Exogenously introgressed and beneficial GSL content made new-type B.napus exhibit the potential for medical exploition and application.Further analysis showed us the seed GSL genetic architecture of new-type B.napus and its similarities as well as differences with normal B.napus.Specific loci for seed GSL content were detected and identified,which could provide theoretical information for rapeseed GSL modification by exogenous genome introgression.And also,all the information would be utilized for elucidating rapeseed GSL genetic architecture.