Analysis Of Lutein Content And Dominant Genetic Loci In Wheat Grains

Lutein is the main component of carotenoids,accounting for 70-90 % of total carotenoids in plants.In human,lutein occurs at high concentration in the macula of the human retina which can effectively filter out blue light,thereby reducing the incidence of cataracts,myopia and retinitis pigmentosa.For instance,lutein is known as the most effective and potential eye-protecting substance.In addition,lutein has high antioxidant capacities and scavenging oxygen free radicals,and also plays an important role in preventing cardiovascular sclerosis,diabetes and tumors caused by aging.At present,due to an aging population and lutein deficiency,more than 2.2 billion people worldwide have encountered irreversible visual impairment and blindness.Wheat is an important food crops with rich germplasm resources and wide planting range.Lutein-rich wheat cultivars could provide valuable lutein supplementation through the daily diet and thus benefit human health.Therefore,developing lutein enriched wheat is a cost-effective strategy to achieve the final goal.In this research,262 Chinese wheat mini-core collections,194 Shanxi wheat collections and 152 DH lines were used to determine the lutein content by high performance liquid chromatography（HPLC）.The effects of different factors on the lutein content in grains were analyzed,and the germplasm resources with high lutein content were screened out.The QTLs related to lutein content in grains were identified by genome-wide association（GWAS）and linkage analysis.The main findings are as follows:1.The lutein content of 262 Chinese wheat mini-core collections in three environments was determined by HPLC.The lutein content in Chinese wheat mini-core collections ranged from 0.87 to 8.90 μg/g,with a difference of about 10 times.Ten cultivars with an average content more than 5.0 μg/g were identified as sources of the high lutein trait.Further studies showed that lutein content among different environments was significantly correlated and the genotype（G）and environment（E）response showed G > G × E > E with the effect of water level likely to be small.These results also demonstrated that the lutein content of Chinese wheat had not undergone extensive selection during the breeding process and was independent of accession type,plant habit,and grain color.However,lutein content was related to the geographical origin of wheat varieties.The lutein content of wheat varieties in Northwest China is higher than that in Southeast China.Among the 11 agronomic traits,only grain traits were significantly correlated with lutein content,among which grain length was significantly positively correlated with lutein,and 1000-grain weight was significantly negatively correlated with lutein content.These results provide reference and guidance for breeding and cultivation of high lutein content varieties.2.By analyzing the lutein content of 194 Shanxi wheat varieties in three environments,it was found that there were three high-content varieties.Lutein content was mainly affected by genotype,and it was less affected by grain color and breeding year.The lutein content of winter varieties was higher than that of spring varieties,and the average content of water land varieties was slightly higher than that of dry land varieties,which further verified that water had little effect on the lutein content of wheat.Heading date,plant height and 1000-grain weight were significantly negatively correlated with lutein content,which may be related to the length of grain filling period.The other 10 agronomic traits had no significant effect on lutein content,which was consistent with the results of Chinese wheat mini-core collection.Genome-wide association analysis found four loci related to lutein content on chromosomes 1B,3A and 7A.These results can provide valuable information for the breeding and cultivation of wheat lutein biofortified varieties in Shanxi Province.3.Since the content of lutein is mainly affected by genetic factors,the genome-wide association（GWAS）of Chinese wheat mini-core collection was performed using a 90 K SNP chip.The results showed that except for 1A,4D and 5B,124 markers on the remaining chromosomes of wheat were significantly associated with lutein content.Six stable genetic loci（QLuc.2A,QLuc.2D,QLuc.3B,QLuc.3D,QLuc.7A and QLuc.7B）were detected in multiple environments,and lutein content increased with the increase of the number of favorable alleles.It indicated that lutein content was controlled by additive effect of multiple locus.Moreover,71 carotenoid metabolism-related candidate genes were identified,among these,8 genes were identified to be different,only CYP97A3 and CCD1 genotypes were significantly associated with lutein content.4.A doubled haploid（DH）population derived from Jinchun 7 and Lin 1219 was used to verify the results of genome-wide association analysis.A total of 3470 markers showing parental differences were used to construct a high-density genetic linkage map.Three major QTLs（Qluc.5A.1,Qluc.5A.2 and QLuc.6A.2）related to lutein content were detected in multiple environments,among which QLuc.6A.2 explained 5.15-10.86 % of the phenotypic variation.The location of Tdurum_contig29936₁20 and Tdurum_contig29936₄00 on chromosome 6A was the same as that of the association analysis.The functional segments of the genetic loci mapped by association analysis and linkage analysis were analyzed.It was found that the functional segments of QLuc.3D,QLuc.7A,QLuc.7B and QLuc.5A contained genes related to carotenoid biosynthesis pathway,which may be involved in the biosynthesis of lutein in common wheat.No known related genes were found in the functional region of QLuc.6A.2,indicating that there are new genes or regulatory pathways related to grain lutein content in hexaploid wheat,which will be the focus of further research in the future.