Improving the tannin composition of grapes

Abstract

This project used genetic manipulation of grapevines as a proof of concept to improve the tannin composition of winegrapes. The efficiency of the system for producing transgenic grapevines was significantly improved and used to alter expression of three key genes of the tannin synthesis pathway. This resulted in altered tannin content and composition in leaves and grapes from the transgenic grapevines. Depending on the gene targeted, the tannin composition was selectively altered in skins or seeds of the berries. Micro-scale fermentation of grapes from the transgenic vines was used to assess the impact on wine colour and tannin.

Summary

Tannins are important for the taste and mouthfeel of wines and together with anthocyanins they form the pigmented polymers that are important for the colour and mouthfeel of red wines. Considerable progress has been made in understanding how tannins are formed in grapes by the flavonoid pathway and identifying some of the key genes that are involved. With the development of techniques for genetically manipulating grapevines, it is possible to alter expression of genes in the tannin pathway to manipulate tannin synthesis in winegrapes. The aim of this project was to determine the potential to improve the tannin content and composition of winegrapes by genetic manipulation of the tannin pathway. The system for transforming grapevine callus tissues to produce transgenic vines was assessed and considerable improvements were made to increase the efficiency of producing transgenic grapevines for evaluation. The refined procedure increased the number of independent plantlets produced from each transformation and also reduced the time taken to produce plantlets and grow the transgenic vines in the glasshouse. However, in many cases it still took up to 3–4 years to get the transgenic vines to produce fruit from potted vines in a glasshouse.