The Research Of Swollen Root Related Genes In Brassica Crops

Turnip(B.rapa),root mustard(B.juncea),and swede(B.napus)are Brassica crops that been domesticated with edible formed swollen fleshy root,and can be used as vegetables,fodder and medicinal materials.Previous analyses of swollen root focused on turnip,but swede and root mustard are rarely been studied.Moreover,genes and molecular mechanisms involved in the formation of swollen root are important to the improvement of the yield of root/stem crops,but have not been revealed.In this study,Chinese cabbage,turnip,leaf mustard,root mustard,swede and rapeseed were used as materials to research the hereditary of swollen root related traits.Some QTLs(quantative trait loci)of swollen root related traits were analyzed with methods of QTL-seq and Euclidean distance.The candidate genes were detected through gene annotation,physical location,expression level,and sequences analysis.The main results are as follow:1.Phenotypic and cytological observation:Phenotypic observation showed that fleshy roots of turnip contained hypocotyls and a part of taproots.The cortex splitting of root was an important sign of rapid thicken of fleshy roots.Histological observation showed that xylem was the main tissue of fleshy roots of turnip.2.Genetic analysis:The populations were constructed from a cross between materials with swollen root and plants with normal root.The phenotype of F₁plants from reciprocal crosses and the distribution of root related traits from segregation populations indicated that the swollen root is a quantitative trait in Brassica.3.QTL mapping of swollen root traits:Two QTLs(FR1.1 and FR7.1),were identified by QTL-seq and genetic linkage analysis in F₂and BC₁P₂populations and were located on A01(4.85-5.00 Mb)and A07(17.31-17.53 Mb).The FR1.1 explained 11.4%of the total phenotypic variations for root diameter,the FR7.1 explained 13.1-23.0%and 16.0-31.0%of the total phenotypic variations in root diameter and root weight,respectively.4.Candidate gene analysis:Bra003652 was selected as the candidate gene among 47 genes in the FR7.1 region(220 kb).Gene Bra003652 located at chromosome A07(17,537,326?17,540,584 bp),and contained a marker(A07?S35)with the highest LOD value;The homologous gene of Bra003652 plays an essential role in cell adhesion and disorganized tumor-like formation in Arabidopsis thaliana;The expression level of Bra003652 in the hypocotyls of turnip was nearly 10times than that of Chinese cabbage.5.Structural analysis of candidate gene:Bra003652 contained eight exons and seven introns,encoded a protein with 684 amino acid.13 SNP variants and one 3bp-base-deletion were detected in the coding region of turnip and Chinese cabbage.Three amino acid variations of the predicted protein sequence from two parents were consistent between turnip and radish,but not consistent with Chinese cabbage and Arabidopsis thaliana,indicating that the amino acid mutations may be related to the formation of swollen root.6.The analysis of swede and root mustard populations:Eight QTLs,which located on B02chromosome with a total length of 5.48 Mb containing 457 candidate genes,were identified based on QTL-Seq and ED analysis in the Brassica juncea population.Four QTLs with a total length of 6.48Mb and 974 candidate genes were identified and located on C09 chromosome in Brassica napus population.Two candidate genes,Bna C09T0017400ZS and Bna C09T0051300ZS,whose homologous genes might involved in the growth and development of swollen hypocotyl/root of rutabaga,were identified.7.Synteny analysis:Synteny analysis was performed among the candidate regions of turnip,root mustard and rutabaga,but no synteny genes were identified,suggesting that the swollen root traits from Brassica species may not be regulated by same genes.The main purpose of the research was to study the cytological characteristics and inheritance of swollen root,and to determine and analysis genes associated with the formation of swollen root in turnip,rutabaga and root mustard.The study will provide more genes resource for the high-yield breeding of swollen root crops and lay the foundation for the research of the molecular mechanism of swollen root formation.