Regulation of Plant Tannin Synthesis in Crop Species

Abstract

Plant tannins belong to the antioxidant compound family, which includes chemicals responsible for protecting biological structures from the harmful effects of oxidative stress. A wide range of plants and crops are rich in antioxidant compounds, offering resistance to biotic, mainly against pathogens and herbivores, and abiotic stresses, such as light and wound stresses. These compounds are also related to human health benefits, offering protective effects against cardiovascular and neurodegenerative diseases in addition to providing anti-tumor, anti-inflammatory, and anti-bacterial characteristics. Most of these compounds are structurally and biosynthetically related, being synthesized through the shikimate-phenylpropanoid pathways, offering several classes of plant antioxidants: flavonoids, anthocyanins, and tannins. Tannins are divided into two major classes: condensed tannins or proanthocyanidins and hydrolysable tannins. Hydrolysable tannin synthesis branches directly from the shikimate pathway, while condensed tannins are derived from the flavonoid pathway, one of the branches of the phenylpropanoid pathway. Both types of tannins have been proposed as important molecules for taste perception of many fruits and beverages, especially wine, besides their well-known roles in plant defense and human health. Regulation at the gene level, biosynthesis and degradation have been extensively studied in condensed tannins in crops like grapevine (Vitis vinifera), persimmon (Diospyros kaki) and several berry species due to their high tannin content and their importance in the food and beverage industry. On the other hand, much less information is available regarding hydrolysable tannins, although some key aspects of their biosynthesis and regulation have been recently discovered. Here, we review recent findings about tannin metabolism, information that could be of high importance for crop breeding programs to obtain varieties with enhanced nutritional characteristics.

The complexities of proanthocyanidin biosynthesis and its regulation in plants

“…PA pathway transcription factors, including MYB, basic helix-loop-helix (bHLH)/MYC, WD40, WRKY, MADS-box, and WIP domain-containingzinc finger family proteins, have been intensively studied across species ( He et al., 2008 ; Yu et al., 2020 ; Wei et al., 2021 ; Mora et al., 2022 ). First discovered in Arabidopsis , the MYB–bHLH–WD40 (MBW) complex, composed of TT2 (MYB123), TT8 (bHLH42), and TTG1 (WD40 family), plays a major role in activating the expression of PA pathway genes, including DFR , ANS , ANR , TT12 ( MATE ), TT13 ( AHA10 ), and TT19 ( GST ) ( Baudry et al., 2004 ).…”

Reducing enteric methane of ruminants in Australian grazing systems – a review of the role for temperate legumes and herbs

“…Tannins are highly polymerised and hydroxylated polyphenol compounds (molecular weight ~500-3000) and they have been historically studied as anti-nutritional factors in relation to animal nutrition (Kumar and Singh 1984) and for bloat prevention (Lees et al 1981;Min et al 2005;Mueller-Harvey 2006). Tannins are a chemically diverse group that comprise two main classes; condensed tannins CT (having a flavan-3-ol base unit and synthesised via the phenylpropanoid pathway) and hydrolysable tannins (HT; characterised as having a gallic acid base unit and synthesised via the shikimate pathway) (Mora et al 2022).…”

“…2005; Mueller-Harvey 2006). Tannins are a chemically diverse group that comprise two main classes; condensed tannins CT (having a flavan-3-ol base unit and synthesised via the phenylpropanoid pathway) and hydrolysable tannins (HT; characterised as having a gallic acid base unit and synthesised via the shikimate pathway) (Mora et al . 2022).…”

Genetic manipulation of anti-nutritional factors in major crops for a sustainable diet in future

“…The initial step involves the condensation of aldols and is catalyzed by 3-deoxy- d -arabino-heptulosonate-7-phosphate synthase (DAHP), with phosphoenol pyruvate and erythrose-4-phosphate as substrates. The synthesis of tannins in plants is often triggered by mechanical wounding or insect attacks ( Mora et al., 2022 ).…”