Looking at Flavonoid Biodiversity in Horticultural Crops: A Colored Mine with Nutritional Benefits

Abstract

Flavonoids represent a wide group of plant secondary metabolites implicated in many physiological roles, from the attraction of pollinators to the protection against biotic or abiotic stresses. Flavonoids are synthetized in a number of horticultural crops that are important components of our daily diet. In the last decades, the consumption of vegetables rich in antioxidants has been strongly promoted from the perspective of prevention/protection against chronic diseases. Therefore, due to their nutritional importance, several attempts have been made to enhance flavonoid levels in species of agronomic interest. In this review, we focus on the flavonoid biodiversity among the major horticultural species, which is responsible of differences among closely related species and influences the qualitative/quantitative composition. We also review the role of flavonoids in the nutritional quality of plant products, contributing to their organoleptic and nutritional properties, and the main strategies of biofortification to increase their content.

Keywords: biodiversity; biofortification; flavonoids; horticultural crops; nutritional quality.

Figure 1

Schematic illustration of the flavonoid biosynthetic pathway, with the main flavonoids in representative horticultural species. Amounts of flavonoids (from USDA database; https://www.ars.usda.gov/nutrientdata [15]) are indicated as a red heatmap ranging from the species with lower to those with higher content. PAL, Phenylalanine ammonia lyase; C4H, cinnamic acid 4-hydroxylase; 4CL, 4-coumarate:coenzyme A ligase; CHS, chalcone synthase; CHI, chalcone isomerase; IFS, isoflavone synthase; FNS, flavone synthase; F3H, flavanone-3-hydroxylase; F3’H, flavanone-3’-hydroxylase; F3’5’H, flavanone-3’5’-hydroxylase; FLS, flavonol synthase; DFR, dihydroflavonol reductase; ANS, anthocyanidin synthase; OMT1, O-methyltransferase 1; GTs, glycosyltransferases; PATs, phenylacyl-transferases.

Figure 2

Flavonoid biofortification by metabolic engineering strategies through the use of structural (blue arrow on the right of the boxes) or regulatory genes’ (green arrow on the left of the boxes) over-expression (OE). The scheme reports the main genes targets studied for flavonoids improvement in horticultural species.