Genetic Analysis And QTL Mapping Of Main Lignans In Schisandra Chinensis

Schisandra chinensis(Turcz.)Baill.is a perennial woody vine plant of Schisandra genus in Schisandraceae.The dried berries are commonly used in China as a precious bulk medicinal material ‘Wuweizi’,which has important medicinal and economic value.Lignan is the main effective component of S.chinensis,which has strong pharmacological activity,and its content is also an important index to evaluate the quality of S.chinensis.Cultivating S.chinensis varieties with high lignan content is of great significance for promoting the development of S.chinensis cultivation industry.Because S.chinensis has the characteristics of complex genetic background,with a long juvenile period and most of the traits are complex quantitative traits,using molecular markers to construct the genetic map and QTL mapping of target traits,and then carry out molecular marker-assisted selection research can greatly shorten the breeding cycle and significantly improve the breeding efficiency.In this study,a large number of polymorphic EST-SSR molecular markers were developed by using the transcriptome sequencing data of S.chinensis.The genetic diversity of S.chinensis accessions was studied and the parents were screened to construct hybrid populations.SLAF-seq technology was used to create a huge number of SLAF markers and construct the first genetic map of S.chinensis.The contents of 6 lignans in fruits and stems of parents and their hybrids were detected in two consecutive years,and their genetic characteristics were analyzed and QTL mapping was performed.The results have important guiding significance for enriching high-quality molecular markers of S.chinensis,analyzing the genetic characteristics of lignans,and promoting directional breeding of S.chinensis.The main findings are as follows:1.A large number of polymorphic EST-SSR markers were developed based on the transcriptome sequencing data of S.chinensis.A total 3421 sets of primers were obtained,and 100 pairs of primers were randomly selected for polymorphism screening,and 28 pairs of polymorphic primers were obtained after screening.Among them,21 pairs of primers with ideal effects were selected to analyze the genetic diversity of 42 accessions in germplasm nursery.The results showed that the number of alleles per locus ranged from 2 to 4,with an average of 2.95,and the average polymorphism information content was 0.43.The genetic distance of 42 accessions ranged from 0.03 to 0.39,with an average of 0.21.2.The contents of 6 main lignans in the fruits and stems of the mapping population were detected in two consecutive years,and the genetic characteristics of lignans in the intraspecific hybrids of ‘Jinwuwei 1’ and ‘Zaohong’ were analyzed.The results showed that the contents of schisandrin,schisandrol B,schisantherin A,deoxyschizandrin,γ-schisandrin and schisandrin C all showed quantitative trait genetic characteristics.Through the mixed genetic analysis of major gene + polygene,it was found that the optimal genetic model for deoxyschizandrin content in fruit was 2MGEA,while the optimal genetic model for other 5 lignans content was 2MG-AD.The optimal genetic models for the contents of schisandrol B,schisantherin A and γ-schisandrin in stems were the same as those in fruits,but the optimal genetic models for the contents of schisandrin A and schisandrin C were different,which were 2MG-A and 1MG-AD,respectively.3.SNP markers were mined using the SLAF-seq method in great quantity.369.2Gb of clean data and 1468.01 M double-end sequencing reads overall were collected.According to the difference between the number of alleles and gene sequences,164109 polymorphic SLAF tags(45.02%)were found.14917 of the polymorphic SLAF tags were heterozygous in the parents and polymorphic between the parents when they were analyzed.4506 SLAF tags were eventually acquired for mapping after additional filtering.4.A high-density genetic linkage map of S.chinensis was successfully constructed for the first time.In this study,three genetic maps were obtained,including maternal genetic map,paternal genetic map and integrated genetic map.The integrated genetic map contained 4027 SLAF markers,with a total length of 2031.83 c M and an average distance of 0.51 c M.The average sequencing depth of the markers on the integrated genetic map was 104.43-fold in the female parent,227.12-fold in the male parent,and 49.64-fold in the F1 generation.High sequencing depth ensures the accuracy of molecular markers.5.A total of 124 QTLs were identified for 6 phenotypic traits in the F1 population of S.chinensis in two years.The LOD threshold range of QTLs detected was 3.00 ～6.29,and the contribution rate of each QTL to the phenotype was 9.30 ～ 18.50%.The QTLs detected in 2021 had four clusters on the linkage group,which were located on LG2,LG6,LG7 and LG12 linkage groups.The QTLs detected in 2022 were clustered into 9 QTLs on the linkage group,which were distributed on LG1,LG3,LG4,LG5,LG6,LG8,LG9,LG12 and LG13.In addition,11 QTLs with stable expression were detected in different years,including 3 QTLs with stable expression of schisandrin content on LG8,LG10 and LG13 linkage groups,and 7 QTLs with stable expression of schisandrol B content on LG3,LG6,LG9,LG10 and LG12 linkage groups.One QTL stably expressed for γ-schisandrin content was located on LG6 linkage group.These QTLs will be the focus of future research.