Study On The Mechanism Of Carotenoid Metabolism And Accumulation In Apricot (Prunus Armeniaca L.) Fruit

Apricot(Prunus armeniaca L.)is a widely cultivated temperate fruit tree with bright color and rich nutrition.Xinjiang is rich in apricot germplasm resources,which is the main production area of apricot in China and even in the world.The variety and content of carotenoids have great influence on the commodity and nutrition of apricot fruit.In this study,the carotenoids in53 Xinjiang apricot germplasm resources were analyzed qualitatively and quantitatively by UHPLC-APCI-MS/MS,and then the physiological and molecular mechanisms of carotenoids accumulation in the fruits of ‘Kuchebaixing' apricot and ‘Shushangganxing' apricot were studied by HPLC-MS/MS,TEM(transmission electron microscopy),RNA-seq(RNA Sequencing)and RT-q PCR(quantitative real-time polymerase chain reaction).The main contents and results are as follows:(1)Based on the metabonomics method of UHPLC-APCI-MS/MS,the carotenoids of 41 apricot cultivars and 12 wild apricot fruits from three populations in Xinjiang were analyzed qualitatively and quantitatively.A total of 13 kinds of carotenes were identified in the peel and flesh of mature fruits,including ?-carotene,?-carotene,(E/Z)-phytoene,violaxanthin,?-carotene,?-carotene,apocarotenal,lycopene,?-cryptoxanthin,neoxanthin,?-cryptoxanthin,lutein and zeaxanthin.The content of total carotenoids in the fruits of 41 apricot cultivars ranged from 20.983 ?g/g FW to 320.278 ?g/g FW.The content of ?-carotene and phytoene in the fruits ranged from 7.356 ?g/g FW to 176.000 ?g/g FW and from 4.970 ?g/g FW to 93.600 ?g/g FW,respectively.The contents of total carotenoids in 12 wild apricot fruits ranged from 70.120 ?g/g FW to 430.006 ?g/g FW.The contents of ?-carotene and phytoene in fruits ranged from 34.900?g/g FW to 200.600 ?g/g FW and from 18.700 ?g/g FW to 232.000 ?g/g FW,respectively.The color of the fruit is orange,and the content of carotenoids is high,while the color of the fruit is white or light yellow,and the content of total carotenoids is the lowest.The main carotenoids in Xinjiang apricot fruits are ?-carotene and(E/Z)-phytoene.In addition,the carotenoid content in wild apricot fruit was generally higher than that in cultivated apricot fruit.Carotenoids in apricot fruits are rich in metabolic diversity.(2)With the ripening of the fruit,the color of the peel of ‘Kuchebaixing' apricot and‘Shushangganxing' apricot changed from green to light yellow and orange respectively,and the color of the flesh changed from green to white and orange respectively.14 kinds of carotene and 27 kinds of carotene lipids were identified from the four development stages of the peel and flesh of the two apricot cultivars.During fruit development,different kinds of carotenoids showed different trends in the peel of two apricot fruits.The contents of total carotenoids in the peel of two apricot cultivars showed significant differences at S3 period.The contents of total carotenoids in the peel of two apricot cultivars were 87.495 ?g/g FW and 221.045 ?g/g FW at S3 period.In S4 period,the difference of total carotenoid content in the peel of ‘kuchebaixing'apricot and ‘shushangganxing' apricot was nearly five times,and the total carotenoid content in the peel was 105.264 ? g/g FW and 497.760 ?g/g FW,respectively.The total carotenoid content in the flesh of two apricot cultivars began to show obvious differences at S3 period,and the difference of carotenoid content in the flesh of two apricot cultivars reached the maximum at S4 period.The difference multiple of total carotenoid content in the flesh of ‘kuchebaixing'apricot and ‘Shushangganxing' apricot was 24 times,and the material causing the greater difference of total carotenoid content in the peel of two apricot cultivars was(E/Z)-phytoene and ?-carotene.Through the observation of plastid development by transmission electron microscope,it was found that the number of plastid globules in the flesh of ‘Shushangganxing'apricot was much more than that of ‘Kuchebaixing' apricot at the late development periods.(3)The total sequencing quality of two apricot varieties was 162.83 Gb by RNA transcriptomics(RNA-seq).The clean data of each sample reached 6 GB.A total of 881 differentially expressed genes were obtained from ‘Shushangganxing' apricot and‘Kuchebaixing' apricot,and 31 structural genes related to carotenoid synthesis were identified.The expression levels of GGPS,PSY,ZDS and Z-ISO,LCYE and NCED1 genes were positively correlated with carotenoid content in apricot pulp,while CCD4 gene was negatively correlated with carotenoid content.(4)Real time quantitative PCR(qRT-PCR)was used to analyze the relative expression of15 carotenoid biosynthesis related genes during the development of ‘Shushangganxing' apricot and ‘Kuchebaixing' apricot.In the flesh of two apricot cultivars,the expression levels of different genes in different periods were different,and the expression levels of two apricot cultivars in the same period were also different.In addition,by comparing the Pearson correlation coefficients of gene qRT-PCR and RNA-seq data in all samples,we can see that the gene expression pattern has a high correlation with RNA-seq,and its change trend is basically the same,which confirms that the transcriptome sequencing data is effective and reliable.