| Chinese cabbage(Brassica rapa L.pekinensis)originated in China and is the vegetable crop with the largest cultivated area and production supply in China.It plays an important role in the annual production,annual supply and stable market of vegetables in China,and has important economic value.Chinese Cabbage,also known as cabbage,is the most important organ for its nutrient reserve and consumption.Leaf-related traits are the economic traits that are considered in the breeding process of Chinese cabbage.It is great significance to realize the molecular breeding of Chinese cabbage and elucidate the genetic and molecular mechanisms of Chinese cabbage leaf development that the QTLs for leaf-related traits in Chinese cabbage.Therefore,in this paper,EST-SSR molecular markers were used to establish the genetic linkage map of Chinese cabbage with the F2 generation segregating population of ZHB×G291,and QTLs for important agronomic traits related to Chinese cabbage yield were constructed.To provide information for exploring important QTL sites that affect Chinese cabbage yield.Trichome are natural physical barriers that Chinese cabbage resists pest infestation,reduces transpiration,and prevents UV rays.Although it plays an important role in the normal growth of Chinese cabbage,people are more likely to choose hairless during the production and sale of Chinese cabbage.Therefore,based on the results of QTL mapping,this study further mapped the burr traits of Chinese cabbage,separated the key regulatory genes,and revealed the role of the gene in the formation of trichomes.At the same time,expression profiling was performed on three tissue parts of cotyledon,true leaf and cauline leaves of Chinese cabbage.The expression changes of related genes were analyzed within the whole genome.The main results were as follows:1.Construction of Genetic Linkage Map of Chinese cabbageWith no burr,glossy Chinese cabbage "ZHB" as the female parent,have burr Chinese cabbage "G291" as the male parent,constructed a F2 segregating population consisting of 240 individual plants.106 EST-SSR markers with polymorphism between the parents were screened from the 500 EST-SSR markers distributed on 10 linkage groups of Chinese cabbage,with a polymorphism of 21%.These markers were anchored to linkage groups and a Chinese cabbage genetic linkage map covering the genome 2270.58 cM was made.2.Investigation and analysis of important agronomic traits in Chinese cabbageThe important field agronomic traits,including Rough weight,Head weight,Longitudinal diameter of head,Transverse diameter of head,Number of outer leaf,Number of head leaf,Length of biggest leaf,Width of biggest leaf,Length of biggest midrib,Width of biggest midrib,Pubesence on leaf surface,were studied.The results showed that rough weight,head weight,longitudinal diameter of head,transverse diameter of head,number of outer leaf,Number of head leaf,Length of biggest leaf,Width of biggest leaf,Length of biggest midrib and Width of biggest midrib were normal distribution in the population,they are Quantitative traits.For the Pubesence on Leaf Surface,the ratio of the number of plants with hair and hairless in the leaves meets the separation ratio of 3:1 and is a quality trait.We analyzed the correlation of these agronomic traits.The results showed that the rough weight had the highest correlation with the head weight,followed by the transverse diameter of head,width of biggest leaf,longitudinal diameter of head,width of biggest midrib,length of biggest leaf,Number of head leaf and Length of biggest midrib,but the correlation between number of outer leaf and head weight is not significant.Therefore,except for number of outer leaf,the above-mentioned related traits are extremely related to the yield of Chinese cabbage,which is an important condition for breeding.3.QTL mapping of impotrtant traits in Chinese cabbageBased on the constructed Chinese cabbage genetic linkage map,QTL mapping was performed on 11 traits,which including rough weight,head weight,longitudinal diameter of head,transverse diameter of head,number of outer leaf,number of head leaf,length of biggest leaf,width of biggest leaf,length of biggest midrib,width of biggest midrib,pubesence on leaf surface.A total of 20 QTLs were mapped.Among them,one QTL locus controlling the rough weight was located on the A03 chromosome;one QTL locus controlling the traits of the head weight was located on chromosome A10;three QTLs related to the number of outer leaf were located on the chromosomes of A03,A04,respectively.Contribution rate of the QTL on A04 was the largest;the QTL associated with the number of head leaf was 1 and located on the A02 chromosome;the QTLs controlling the length of biggest leaf were the most,with the chromosome AO 1、A02,A04,A09 and A10,two on the A03 chromosome,with one QTL locus having the highest contribution rate of 19.8%;three QTLs controlling the width of biggest leaf,located at chromosome A02.A05 and A10,and the QTL contribution rate on the A05 chromosome was the largest;The QTLs associated with length of biggest midrib were 3 and located on chromosome A02,A08,and A09,and the largest contribution rate was on chromosome A09;One locus related to pubesence on leaf surface was located on chromosome A06,and its contribution rate was 47%。The QTL loci of longitudinal diameter of head,transverse diameter of head and Width of biggest midrib not found in this paper.4.Fine Mapping of trichome Genes in Chinese cabbage and cloning,marker development and validation of candidate genesThe F2 segregation population was further expanded to 1456,and the trichome traits were identified and fine-grained.The results showed that the burr traits of Chinese cabbage were controlled by a single dominant gene(χ2 =1.06<3.841).The SSR markers on the A06 linkage group were encrypted,and the genes controlling leaf trichome were finely mapped between the A6S95-A6S103 markers.The physical distance was 0.55 Mb,and a candidate gene BraGL1 was screened from it.The CDS sequence,genomic sequence,and promoter sequence of the gene were cloned and sequenced.Compared with the control Chinese cabbage cultivar "G291",the hairless"ZHB" has a 5 base deletion in the third exon region,leading to early termination of protein translation,which may result in loss or alteration of the gene’s function,resulting in a burr-free phenotype;and there is a 12 bases in the promoter region,too.The expression level of BraGL1 gene of the "ZHB" was significantly higher than that of the "G291”.Deletions may affect their transcription levels and and it is needed for further study.Based on the sequence differences of the BraGL1 gene in the two parents in the CDS region and promoter region,two InDel markers were developed and validated in the F2 segregating population,commercial cabbage species,and Chinese cabbage inbred germplasm resources.The two markers were found to be completely linked to the leaf trichome phenotype.5.Expression profiling of cotyledon,true leaf and stem leaf of Chinese cabbageA total of 430.59 Mb clean reads were obtained from the cotyledon,true leaf and stem leaf of the Chinese Cabbage "LB-F2".A total of 35,305 differentially expressed genes were detected.The results showed that the genes involved in regulating the trichome traits of Chinese cabbage were mainly concentrated on the plant hormone signal transduction pathway.GL3,EGL1 and SAD2 may jointly regulate the occurrence and development of the epidermal hair of Chinese cabbage. |
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