Mapping Skin Color Related Genes In Watermelon

Watermelon?Citrullus lanatus?is a horticultural crop widely cultivated all over the world.It is rich in high nutritional value and plays an important role in the economic development of China.Skin color is one of the most important appearance quality of watermelon.Watermelons sold in the market are mainly green skin,yellow skin watermelon appeared in recent years,has been favored by consumers.Therefore,the research of watermelon skin color has been paid more and more attention by national and foreign researchers,and the cultivation of watermelon varieties with various skin colors has become one of the important tasks of watermelon quality breeding.In this experiment,female parent 1025?yellow skin?and female parent 783?dark green skin?were used to construct F₂ population with male parent COS?light green skin?respectively,and the extreme traits were selected to construct gene pool: The yellow-green gene pool of skin and the deep-light gene pool of skin were sequenced.The target chromosome or region which controlled the color gene of watermelon skin was obtained by BSA sequencing results,and the CAPS markers were developed by bioinformatics,using the genome resequencing data of parents.The genetic linkage map was constructed by using the phenotypic data of F₂ generation mapping population combined with polymorphic CAPS markers,and the genetic linkage analysis of color traits of watermelon skin was carried out to obtain the linkage markers and mapping interval of skin color.The main results of this experiment are as follows:Through field investigation and genetic analysis of six generations of 1025 and COS populations,it was found that both F₁ and BC₁P₁ had yellow skin,the segregation ratio of skin yellow to green watermelon in F₂,BC₁P₂ obeys Mendelian Law of Genetics by chi-square test.The results showed that yellow skin of watermelon was a quality trait controlled by a single gene,and yellow skin was dominant to green.The results of BSA analysis showed that the yellow gene controlling skin was mapped to the front of chromosome 4,and primers were designed for chromosome 4.The polymorphic CAPS markers combined with F₂ population was used to construct genetic map,and the gene controlling the yellow skin of watermelon was located in the463,476 bp-574,590 bp interval of the front of chromosome 4,and the qsc-1 was located between the two CAPS markers W4-2 and W4-01,genetic distance was 2.0c M.A total of 7 genes?Cla002767-Cla002773?were found in the candidate interval,functions of 6 genes are unknown.Cla002769 is associated with Magnesium chelatase subunit,and Magnesium chelatase is the key enzyme in the process of chlorophyll synthesis.Therefore,it is concluded that Cla002769 is a candidate gene to determine the yellow skin of watermelon.Skin color of F₁ generation of 783 and COS showed the intermediate characters of two parents,but its skins tended to be dark green and F₂ population showed continuous variation infield,which indicated that the green depth of watermelon skin was a quantitative character regulated by several genes,and the dark green skin was not completely dominant to the light green of watermelon skin.The target chromosomes were determined to be 9 and 10 by BSA sequencing,and no QTL locus was detected on chromosome 10 related to the green depth of skin by subsequent experiments and QTL analysis,but in the 13,122,025 bp-13,428,612 bp region of chromosome 9,a major effect QTL?qsc-2?was identified,which was located between the two markers W9-02 and W9-03,and the genetic distance was 3.97 c M,the LOD value of the locus was 25,and the contribution rate was 69.16%,the additive effect value was-0.4114.A total of 12 genes?Cla016133-Cla016145?were found in the candidate interval,functions of 4 genes are unknown.Other gene functions are related to cell wall metabolism,cellulose formation,mitochondrial formation,cell signal transduction,plant resistance to stress,electron transfer of light,nuclear membrane metabolism,and so on.