The Genetic Studies Of Pulp Color And Mapping Of QTL For Carotenoids Content In Citrus

Citrus fruit contains abundant carotenoids,and the carotenoid composition and content are decisive factors for exterior quality,fruit nutritional property and health function to some extent.As a perennial woody plants,the long juvenile period,the polyembryony in most citrus cultivars,impacted the hybridization as well as the segregating population construction for genetic analysis.At present,work on the genetic mechanism and QTL of carotenoid for citrus pulp is still rare.More than 10 years ago,Dr.Tian meilian in the laboratory used C.reticulata as the female parent,Poncirus trifoliata as the male parent,via embryo rescuing and identification of molecular markers,She cretaed an F₁ hybrid population.And this population began to set fruits years ago.Later,we have got the genetic map of this population,as provides an foundation for our following genetic research and QTL mapping.In this study,we measured the color index?CCI?and ran High Performance Liquid Chromatography?HPLC?for conducting a preliminary explore of physiological basis and genetic characteristics of citrus pulp color diversity.By using high density genetic linkage map for carotenoids metabolic QTL,we got a number of genetic loci associated with carotenoid contents.The mian results were as follows:1.Analysis of physiological basis and genetic characteristics of the pulp color diversity in C.reticulata×Poncirus trifoliata hybrid populationWe measured the color index?CCI?in the hybrid F₁ group.The results showed that the pulp color was a quantitative trait.We conduct High Performance Liquid Chromatography?HPLC?for C.reticulata,Poncirus trifoliata and the hybrid population.In Poncirus trifoliata,we found that the content of different carotenoids varied among plants,and the same carotenoid in every offspring is also different.By conducting normal test for all the carotenoid content and total carotenoid content,we found that all carotenoids are normal or skewed normal distribution,this indicated each kind of carotenoid was controlled by multiple genes.we used color index with total carotenoid content and each carotenoid content for correlation analysis.Results showed that?-cryptoxanthin,auroxanthin,zeaxanthin,lutein,unknown-3,unknown-4,these six kinds carotenoid were positive correlation with color index,the total carotenoid content was positively correlated with the color index.By correlation analysis of the color index and each carotenoid accounted for the proportion of total carotenoids,we found that the proportion of zeaxanthin,lutein,unknown-4 is positively related to color index,the proportion of phytoene and phytofluene is negatively related to color index.According to the gene expression analysis of carotenoid metabolism pathway,We found that DXS and IPI genes had significant difference between the two extreme pools,these two genes were involved in the synthesis of GGPP,a carotenoid precusor substance.PSY,LCYB1,HYD genes have a higher expression in deep-color flesh than light-color.2.QTL analysisThis study detected eight carotenoids QTL loci distributing on five chromosome.In the detected loci,seven carotenoids and the total carotenoid were located in the same interval in chromosome2,also the chromosome3 and chromosome9,which suggested that a commom genetic factor determining the diversity of carotenoids.According to the results of gene relative expression,this study found seven genes differentially expressed between extreme phenotype pool,and these genes were in the positionong interval.The seven genes were further verified by growth period patterns,and two candidate genes were screened out which have high correlation with pulp color.The gene number were:Ciclev10019730m,Ciclev10021268m.We cloned the 5'upstream sequence and coding sequence of gene Ciclev10019730m,Ciclev10021268m from C.reticulata and Poncirus trifoliata.We found Ciclev10019730m gene had an allelic polymorphism in C.reticulata,one of the alleles at the base 1475th,an 14bp sequence is missing,but in Poncirus trifoliata this missing was not found.The promoter of Ciclev10021268m had allelic polymorphism in Poncirus trifoliata,one of the alleles missed 156bp between-1842bp to-1686bp,and had a 636bp insertion in-1373bp to-737bp at the same time.However,another allele for this gene had no missing,and the sequence is almost the same as C.reticulata.