Investigation of bitter compounds in Idesia polycarpa and identification of associated biosynthetic genes

Abstract

Idesia polycarpa, a notable woody oil plant indigenous to China and Northeast Asia, is characterized by a distinctly bitter flavor in most of its tissues and oil, which restricts the potential applications of its derived products in the food sector. In this study, we utilized a metabolomics approach to contrast the bitter crude oil with the bitterness-free refined oil, discovering that naringin was prevalent in the crude oil but absent in the refined version. We also pinpointed crucial genes involved in the biosynthesis of naringin in the I. polycarpa genome, which include: Five PAL genes, three C4H genes, four 4CL genes, four CHS genes, two CHI genes, five 7-Glct genes, and two 1,2Rhat genes. The role of these candidate genes in naringin production was assessed through virus-induced gene silencing (VIGS) assays in Idesia seedlings, revealing that the CHS and 1,2Rhat genes are vital for naringin biosynthesis. Furthermore, in vitro assays validated the enzymatic activity of 1,2Rhat1 and 1,2Rhat2, while molecular docking analysis pinpointed key amino acid residues crucial for their catalytic activity. In summary, we identified naringin as a primary bitter component in I. polycarpa oil and functionally characterized its biosynthetic genes, offering valuable genetic resources for mitigating bitterness in I. polycarpa oil.