| Apricot(Prunus armeniaca L.)is an important Rosaceae family fruit tree,its fruit not only bring the feast of vision,smell and taste to consumers,but also meet the daily needs of the human body.In these quality factors,flavor and color play the leading role on consumption,therefore,it is necessary that deeply mining genes related to apricot fruit flavor,color quality formation and analyzing its transcriptional regulation mechanism,which will have vitally important scientific and practical significance for quality improvement and regulation of apricot fruit.In the present study,we took Xinjiang apricots as our materials.The composition and content of flavor compounds,including soluble sugar,organic acid and aroma volatiles,in reddish apricot “Jianali” with great change in flavor quality during fruit ripening were determined by(High Performance Liquid Chromatography,HPLC)and(Gas Chromatography-Mass Spectrometry,GC-MS).The constituent and content of carotenoids in three different color types(totally 6 varieties)of apricot were detected by HPLC.RNA-sequencing was conducted on the Illumina Hiseq 2000 platform by taking “Jianali” and “Luntaixiaobaixing” apricots as materials.The structure genes,transcription factors and preliminary transcriptionally regulated network of flavor and color quality formation were identified by homologous comparison and WGCNA(Weighted Gene Co-expression Network Analysis).The main results are as follows:1.Sucrose,fructose,sorbitol and glucose were the dominant soluble sugars in apricot fruit.Sucrose accounted for 60 % of the total sugar.Finally,25 differentially expressed genes of sugar metabolism were identified by integrating transcriptomic and metabolomic method.Among them,PaSPS,PaSUS,Pa Ivr,PaHXK,PaFRK,PaPFK1 were the key genes responsible for the increase of the sugars content during fruit ripening.Malic acid,quinic acid acid and citric acid took the largest proportion of the total organic acid.And the percentage of malic acid were 66 %.Thirty-nine differential expression genes(DEGs)related organic acid metabolism were annotated.Synergetic expression of PaNAD-MDH、PaPK、PaPDC、PaPEPC、PaACO、PaSDH、PaSTK、PaIDH resulted in a decrease of organic acids during fruit ripening.At the same time,19 sugar transport proteins and 5 organic acid transport proteins were identified.Among them,PaSWEET、PaSTP、PaERDL and PaALMT、PaSFC1 involved in sugar and organic acid transportation in apricot.2.β-ionone,γ-decanolide and(Z)-3-hexenyl acetate are characteristic aroma components of apricot fruits and they increased significantly with fruit ripening.PaFAD was the key gene of lactone formation in fatty acid pathway,PaLOX was the crucial gene of ester formation in terpenoids pathway,PaCCD play the crucial role in apocarotenoid aroma volatiles formation in terpenoids pathway.Based on expression of these genes,terpenoids aroma compounds and C6 aroma compounds declined with the fruit maturation,while the contents of apocarotenoids aroma volatiles,lactone and esters risen.3.WGCNA analysis revealed that the three modules " red" " cyan" " blue" were closely correlated with flavor compounds.Fifteen transcription factors and 6 abscisic acid receptors were identified as candidate regulators for flavor compounds accumulation by WGCNA and Cytoscape visualization.Finally,Pa ERF,PaABAR and PaMADS-box were inferred that regulated the accumulation of flavor compounds.4.Totally,six carotenoids including violaxanthin,lutein,neoxanthin,phytotene,β-cryptoxanthin and β-carotene were identified from three different color type of apricots.The contents of violaxanthin and lutein dropped with the fruit maturation.Nevertheless,the accumulation of neoxanthin,phytotene,β-cryptoxanthin and β-carotene increased rapidly.Interestingly,β-carotene and β-cryptoxanthin in reddish orange variety “hongyuxing” and “danxing” was higher than them in yellow and light yellow cultivars.Therefore,we inferred that β-carotene and β-cryptoxanthin might be the predominat component of red and orange cultivars.And their color depends on the concentration of β-carotene and β-cryptoxanthin.WGCNA indicated that "blue" and "lightgreen" modlues correlated significantly with carotenoids in red-peel “Jianali” apricot,"blue" and "turquoise" modlues with carotenoids in “Luntaixiaobaixing” apricot.PaDXS,PaPSY,PaCRTISO,Pa LCYB,PaCHYB,PaNCED were identified as the key genes responsible for carotenoid metabolism,in which PaCCD4 presented the negative regulation role on color accumulation.Three PaCCD4 genes were identified in this study,and the expression of PaCCD4 in the white flesh of “Luntaixiaobaiixng” was higher than that in red peel of “Jianali”.Based on that,it was inferred that PaCCD4 was the main factor resulting in the formation of white-flesh apricot fruit.5.A series of transcriptional factor(TFs),including three PaAP2 TFs related to ethylene,two PaARF4 relevant with indoleacetic acid signal transduction,six PaBZR1 related to brassinolide and three PaPIF1 correlated to phytochrome,two PaGLK2 relevant with plastid,four PaDDB1、nine PaCOP1 related to light signal transducrion,were identified as the hub gene in the co-expression network.PaAP2,PaARF4,PaBZR1,PaGLK positively regulated carotenoid accumulation,however,PaPIF1、PaDDB1、PaCOP1 negatively regulated carotenoids accumulation. |
