Transcriptomic and metabolomics of flavonoid compounds in Actinidia arguta var. arguta

Actinidia arguta (Sieb. et Zucc.) Planch ex Miq. is fruit plant with high added value, rich in bioactive compounds relevant for human health, like flavonoids and vitamin C, and has high antioxidant activity. These flavonoids also play important roles in plant immune responses and have strong medicinal implications. Moreover, it is very widely distributed in China and attracted more attention with great economic significance in recent years. However, the majority of research on flavonoids has been focused on fruit, not much has been elucidated in leaf in A. arguta. Whether are the leaves of Actinidia arguta also rich in flavonoids and other biologically active ingredients? The metabolome and transcriptome in fruits and leaves of A. arguta var. arguta cv. Changjiang No.1 (CJ-1) was analyzed in this study. We detected ten flavonoids in CJ-1 leaves that belonged to quercetin, isorhamnetin and kaempferol and using LC-MS/MS technology. Flavonoid quercetin were all detected in five tissues. Flavonoid qualification indicated that total flavonoids in young apical leaves were the highest (10219.84 µg·g−1) and 129.8 folds than in fruits (78.75 µg·g−1). From the transcriptome data, we obtained 70,631 non-redundant unigenes in total. There were 32,593 differentially expressed genes (DEGs) to be identified, including 29,617 up-regulated and 2976 down-regulated genes in fruits and young apical leaves. There were 127 metabolic pathways enriched with 3567 DEGs, in which 45 DEGs were associated with flavonoid biosynthesis. Next, the expression of qRT-PCR of key flavonoid pathway genes in leaves were higher than that in other tissues, which was consistent with the higher total flavonoid level. The data provided here were valuable for knowing the molecular mechanisms of flavonoids accumulating in different tissues. Our results were of significant contribution to the literature as they proposed possible new insights of applying leaves in A. arguta in the food and healthcare industries for their high content of flavonoids.