Identification of Key Genes Controlling Carotenoid Metabolism during Apricot Fruit Development by Integrating Metabolic Phenotypes and Gene Expression Profiles.

To explore the metabolic basis of carotenoid accumulation in different developmental periods of apricot fruits, targeted metabonomic and transcriptomic analyses were conducted in four developmental periods (S1-S4) in two cultivars (Prunus armeniaca cv. "Kuchebaixing" with white flesh and P. armeniaca cv. "Shushangganxing" with orange flesh) with different carotenoid contents. 14 types of carotenes and 27 types of carotene lipids were identified in apricot flesh in different developmental periods. In S3 and S4, the carotenoid contents of the two cultivars were significantly different, and ß-carotene and (E/Z)-phytoene were the key metabolites that caused the difference in the total carotenoid content between the examined cultivars. Twenty-five structural genes (including genes in the methylerythritol 4-phosphate and carotenoid biosynthesis pathways) related to carotenoid biosynthesis were identified among the differentially expressed genes in different developmental periods of the two cultivars, and a carotenoid metabolic pathway map of apricot fruits was drawn according to the KEGG pathway map. The combined analysis of carotenoid metabolism data and transcriptome data showed that PSY, NCED1, and CCD4 were the key genes leading to the great differences in the total carotenoid content. The results provide a new approach to study the synthesis and accumulation of carotenoids in apricot fruits.

Phylogeography of Prunus armeniaca L. revealed by chloroplast DNA and nuclear ribosomal sequences.

To clarify the phytogeography of Prunus armeniaca L., two chloroplast DNA fragments (trnL-trnF and ycf1) and the nuclear ribosomal DNA internal transcribed spacer (ITS) were employed to assess genetic variation across 12 P. armeniaca populations. The results of cpDNA and ITS sequence data analysis showed a high the level of genetic diversity (cpDNA: HT = 0.499; ITS: HT = 0.876) and a low level of genetic differentiation (cpDNA: FST = 0.1628; ITS: FST = 0.0297) in P. armeniaca. Analysis of molecular variance (AMOVA) revealed that most of the genetic variation in P. armeniaca occurred among individuals within populations. The value of interpopulation differentiation (NST) was significantly higher than the number of substitution types (GST), indicating genealogical structure in P. armeniaca. P. armeniaca shared genotypes with related species and may be associated with them through continuous and extensive gene flow. The haplotypes/genotypes of cultivated apricot populations in Xinjiang, North China, and foreign apricot populations were mixed with large numbers of haplotypes/genotypes of wild apricot populations from the Ili River Valley. The wild apricot populations in the Ili River Valley contained the ancestral haplotypes/genotypes with the highest genetic diversity and were located in an area considered a potential glacial refugium for P. armeniaca. Since population expansion occurred 16.53 kyr ago, the area has provided a suitable climate for the population and protected the genetic diversity of P. armeniaca.

Transcriptome analysis insight into ethylene metabolism and pectinase activity of apricot (Prunus armeniaca L.) development and ripening.

Ethylene metabolism is very important for climacteric fruit, and apricots are typical climacteric fruit. The activity of pectinase is closely related to fruit firmness, which further affects fruit quality. To better understand ethylene metabolism, pectinase activity and their molecular regulation mechanisms during the development and ripening of apricot fruit, ethylene metabolism, pectinase activity and the "Luntaibaixing" apricot fruit transcriptome were analyzed at different developmental stages. Ethylene metabolic precursors, enzyme activities and ethylene release increased during fruit development and ripening, with significant differences between the ripening stage and other stages (P < 0.05). Fruit firmness decreased significantly from the S1 to S5 stages, and polygalacturonase, pectin methylesterase, and pectin lyase activities were significantly higher in the S5 stage than in other stages. RNA sequencing (RNA-seq) analysis of fruit resulted in the identification of 22,337 unigenes and 6629 differentially expressed genes (DEGs) during development and ripening, of which 20,989 unigenes are annotated in public protein databases. In functional enrichment analysis, DEGs among the three stages were found to be involved in plant hormone signal transduction. Four key genes affecting ethylene metabolism, six key ethylene signal transduction genes and seven genes related to pectinase in apricot fruit were identified by KEGG pathway analysis. By RNA-sequencing, we not only clarified the molecular mechanism of ethylene metabolism during the ripening of "Luntaibaixing" apricot fruit but also provided a theoretical basis for understanding pectin metabolism in apricot fruit.

Analysis of carotenoid content and diversity in apricots (Prunus armeniaca L.) grown in China.

The carotenoids in the peel and flesh of 41 apricot cultivars were qualitatively and quantitatively analysed by UHPLC-APCI-MS/MS, and the L*, a*, b* and quality indexes of the fruits were determined. The results showed that the L*, a*, b* and quality indexes of the fruits were quite different, and 13 carotenoids were detected in the peel and flesh of apricots, among which ε-carotene, α-cryptoxanthin and apocarotenal were newly detected carotenoids in apricots. The total carotenoid content of the 41 apricot cultivars varied from 20.983 to 320.278 µg/g FW, and the total carotenoid content varied from 17.353 to 222.098 µg/g FW in the peel and from 2.536 to 98.179 µg/g FW in the flesh. The main components of apricot fruits were ß-carotene and (E/Z)-phytoene, followed by ß-cryptoxanthin and lutein. This study shows that carotenoids in apricot fruits have rich metabolic diversity.