Combined transcriptomic and metabolic analyses reveal potential mechanism for fruit development and quality control of Chinese raspberry (Rubus chingii Hu).

KEY MESSAGE: Combined transcriptomic and metabolic analyses reveal that fruit of Rubus chingii Hu launches biosynthesis of phenolic acids and flavonols at beginning of fruit set and then coordinately accumulated or converted to their derivatives. Rubus chingii Hu (Chinese raspberry) is an important dual functional food with nutraceutical and pharmaceutical values. Comprehensively understanding the mechanisms of fruit development and bioactive components synthesis and regulation could accelerate genetic analysis and molecular breeding for the unique species. Combined transcriptomic and metabolic analyses of R. chingii fruits from different developmental stages, including big green, green-to-yellow, yellow-to-orange, and red stages, were conducted. A total of 89,188 unigenes were generated and 57,545 unigenes (64.52%) were annotated. Differential expression genes (DEGs) and differentially accumulated metabolites (DAMs) were mainly involved in the biosynthesis of secondary metabolites. The fruit launched the biosynthesis of phenolic acids and flavonols at the very beginning of fruit set and then coordinately accumulated or converted to their derivatives. This was tightly regulated by expressions of the related genes and MYB and bHLH transcription factors. The core genes products participated in the biosynthesis of ellagic acid (EA) and kaempferol-3-O-rutinoside (K-3-R), such as DAHPS, DQD/SDH, PAL, 4CL, CHS, CHI, F3H, F3'H, FLS, and UGT78D2, and their corresponding metabolites were elaborately characterized. Our research reveals the molecular and chemical mechanisms of the fruit development of R. chingii. The results provide a solid foundation for the genetic analysis, functional genes isolation, fruit quality improvement and modifiable breeding of R. chingii.