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 β-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.
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.
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