Abstract
The polyphenol family encompasses several classes of molecules corresponding to different branching points of the biosynthetic pathway. Citrus plants produce large amounts of phenolic compounds, especially flavanones, flavones and coumarins. Some of them are specific to Citrus. In Citrus, these bioactive compounds are involved in fruit quality as well as in plant defense and therefore are a target of breeding programs with some compounds being desired and some others avoided. Many studies have characterized their composition in Citrus. However, few studies reported several classes of polyphenols in a single analysis. In addition, although phenolic compounds vary strongly with developmental and environmental conditions, these factors are often omitted thus preventing comparative analyses. To overcome these problems, we took care to collect plant organs experiencing similar environmental conditions. This step is essential to link biochemical data to the key steps of the pathway involved in genetic variability or shifts in metabolite biosynthesis in different tissues. Then, we developed a high-throughput procedure that permitted rapid reconstruction of the distribution of main classes of soluble polyphenols in contrasting tissues and genotypes. We evidence that the combination of datasets from contrasting tissues improved cultivar classification based on polyphenol contents. Drawing a map of the distribution of phenolic compounds across cultivars highlights potential regulatory nodes of the biosynthetic pathway. In addition to the steps catalyzed by rhamnosyltransferases, we proposed that the steps catalyzed by phenylalanine ammonia-lyase, the step conducing to 2',4'-dihydrocinnamic acid from p-coumaric acid and the step involving flavone synthase were important regulatory nodes in in “Clementine” and “Star Ruby” grapefruit.