Abstract
To assess the interrelation between the change of metabolites and the change of fruit color, we performed a combined metabolome and transcriptome analysis of the flesh in two different Actinidia arguta cultivars: “HB” (“Hongbaoshixing”) and “YF” (“Yongfengyihao”) at two different fruit developmental stages: 70d (days after full bloom) and 100d (days after full bloom). Metabolite and transcript profiling was obtained by ultra-performance liquid chromatography quadrupole time-of-flight tandem mass spectrometer and high-throughput RNA sequencing, respectively. The identification and quantification results of metabolites showed that a total of 28,837 metabolites had been obtained, of which 13,715 were annotated. In comparison of HB100 vs. HB70, 41 metabolites were identified as being flavonoids, 7 of which, with significant difference, were identified as bracteatin, luteolin, dihydromyricetin, cyanidin, pelargonidin, delphinidin and (−)-epigallocatechin. Association analysis between metabolome and transcriptome revealed that there were two metabolic pathways presenting significant differences during fruit development, one of which was flavonoid biosynthesis, in which 14 structural genes were selected to conduct expression analysis, as well as 5 transcription factor genes obtained by transcriptome analysis. RT-qPCR results and cluster analysis revealed that AaF3H, AaLDOX, AaUFGT, AaMYB, AabHLH, and AaHB2 showed the best possibility of being candidate genes. A regulatory network of flavonoid biosynthesis was established to illustrate differentially expressed candidate genes involved in accumulation of metabolites with significant differences, inducing red coloring during fruit development. Such a regulatory network linking genes and flavonoids revealed a system involved in the pigmentation of all-red-fleshed and all-green-fleshed A. arguta, suggesting this conjunct analysis approach is not only useful in understanding the relationship between genotype and phenotype, but is also a powerful tool for providing more valuable information for breeding.
Highlights
Kiwifruit (Actinidiaceae, genus Actinidia), a kind of perennial and deciduous plant, is one of the fruit trees that have been domesticated and cultivated successfully in the last century, and in recent years has been grown commercially worldwide [1,2]
Metabolomic analysis can be used to investigate the relationship between biological processes and phenotypes; some intuitive changes can be observed at the metabolic level [32]
The focus of our research was on flesh coloring, so the HB100 vs. HB70 comparison was selected as the object for further analysis
Summary
Kiwifruit (Actinidiaceae, genus Actinidia), a kind of perennial and deciduous plant, is one of the fruit trees that have been domesticated and cultivated successfully in the last century, and in recent years has been grown commercially worldwide [1,2]. Flavonoids, secondary metabolites found in plants, contribute to plant environmental adaptation [6], fruit development [7,8], and even human health [9] These compounds accumulate in various tissues at different developmental stages [10], and they are the direct factors that cause red color in Actinida flesh [11,12,13]. Through integrated analysis of identified metabolites with significant difference and related genes involved in flavonoid biosynthesis, the association between metabolites and genes was explained so as to provide valuable information for revealing the red coloring of A. arguta
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