Transcriptomics and metabolomics reveal the underlying mechanism of drought treatment on anthocyanin accumulation in postharvest blood orange fruit
Background: Anthocyanins are the most important compounds for nutritional quality and economic values of blood orange. However, there are few reports on the pre-harvest treatment accelerate the accumulation of anthocyanins in postharvest blood orange fruit. Here, we performed a comparative Transcriptome and metabolomics analysis to elucidate the underlying mechanism involved in seasonal drought (SD) treatment during fruit expansion stage on anthocyanin accumulation in postharvest 'Tarocco' blood orange fruit. Results: Our results showed that SD treatment slowed down the fruit enlargement and increased the sugar accumulation during fruit development and matured period. Obviously, under SD treatment, the accumulation of anthocyanin in blood orange fruit during postharvest storage was significantly accelerated and markedly higher than that in CK. Meanwhile, the total flavonoids and phenols contents and antioxidant activity in SD treatment fruit were also sensibly increased during postharvest storage. Based on metabolome, we found that substrates required for anthocyanin biosynthesis, such as amino acids and their derivatives, and phenolic acids, have significantly accumulated and higher in SD treated mature fruit compared with that of CK. Further according to the results of transcriptome data and weighted gene coexpression correlation network analysis (WGCNA) analysis, phenylalanine ammonia-lyase (PAL3) was considered key structural gene. qRT-PCR analysis verified that the PAL3 was highly expressed in SD treated postharvest stored fruit and was significantly positively correlated with the anthocyanin content. Moreover, we found that other structural genes in anthocyanin biosynthesis pathway were also upregulated under SD treatment through transcriptome data and qRT-PCR analysis. Conclusions: The findings suggest that SD treatment promotes the accumulation of substrates necessary for anthocyanin biosynthesis during fruit ripening process, and activates the expression of anthocyanin biosynthesis pathway genes during postharvest storage period, especially PAL3, co-contributed to the rapid accumulation of anthocyanin. The present study provides a theoretical basis for postharvest quality control and water-saving utilization of blood orange fruit. Overall design: Comparative gene expression profiling analysis of RNA-seq data for drought treated and control postharvest 'Tarocco' Blood orange