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Tailoring new grapevine varieties for the wine industry
Nuevas variedades de vid adaptadas a la industria vinícola
Isak S. Pretorius
The Australian Wine Research Institute
Adelaide, Australia

Grapevine constitutes one of the most important fruit species globally, thanks to its remarkable propagation characteristics. Evolving from a bushy plant to a trailing climber, this ancient species has been domesticated with ease, and its fruit is today the basis for major worldwide industries.

Desirable traits in vines have long been identified as critical to wine quality. Unfortunately the complex network of genes that control these desirable traits also complicate traditional breeding programmes. It is currently believed that the efforts of the grapevine industries to preserve and encourage desirable characteristics can accentuate the shortcomings of practices that have traditionally allowed for sustainable yields.

From an economic viewpoint, sustainable, high-quality production is a direct consequence of the fitness of vines in the context of their available environmental resources. It is widely believed that there is immense potential for enhanced cost-effective production of grapes and wine with minimised resource inputs, improved quality and low environmental impact. Among a host of factors at play in enhancement efforts include improved nutrient capture from soils and better adaptation to adverse conditions. Cultivation practices could benefit from enhanced phytosanitary features of cultivars, resulting in the reduced use of agrochemicals and fungicides. But the availability of excellent starting material is fundamental to establishing new or replacement vineyards; germplasm maintenance and propagation is key.

The fundamental principles of grapevine cultivation and winemaking have remained the same for millennia, while the role of wine has changed dramatically, from a practical, storable beverage, to a cultural luxury product, placing wine between market-pulling forces and technology-pushing developments, between tradition and innovation. This metamorphosis of the global wine sector has resulted in a fundamental change in the focus of research and development activities of the leading wine-producing countries.

New initiatives are being seized from recombinant DNA technology; extensive efforts are underway to characterise the genomes of agriculturally important species. Grapevine biotechnology is currently practised in all major viticultural research centres worldwide, several technical factors dictating the speed of the progress being made. The success rate has increased exponentially over the last few years, focussing research activities on some of the most interesting traits of genetically modified grapes and creating huge potential for the wine industry.

Improvement of methods for the transformation of grapevines

The grapevine genome is huge and complex, and its accessibility is currently relatively restricted. This will soon be overcome by the intense study being performed on it and the number of initiatives working on molecular markers for the Vitis genome.1

New molecular techniques, such as bombardment technologies, are enabling the addition of interesting genes into plant genomes, and are opening up new possibilities for plant improvement in grapevine. The first significant progress was made when embryonic cell lines were used as target tissue for transformations, leading to routine production of transgenic grapevines, involving a few commercially important grapevine scion and rootstock cultivars.2,3 Figure 1 depicts a summary of the processes involved in grapevine transformation, as well as a time scale of the individual components of the process.

Targets for genetic improvement

Despite the limited successes achieved in early attempts to introduce genes with known functions into plant species to express a desired phenotype, the use of molecular biology to study fundamental processes and to combine process knowledge with application has produced a growing list of genes and their regulatory sequences from economically important species, including grapevine.

Disease resistance, and other factors impacting cultivation and quality are the main targets for genetic improvement of grapevine cultivars and rootstocks, as indicated in Table 1. Several approaches have been used to enhance disease tolerance in plants, almost all of them making use of some part of the natural interaction between host and pathogen. Most transformation strategies involve the introduction into the host, at high copies or in an inducible manner, of a gene that produces anti-pathogenic activity, to optimise the plant defence response. Also, disease tolerance can be improved by expressing a pathogen–derived gene at an inappropriate time or in an inappropriate form or amount during the infection cycle, thus preventing the pathogen from maintaining infection. This is the case in most antiviral strategies applied in grapevine genetic improvement research.

Transgenic approaches have also speeded up the development of plant lines able to adapt to adverse climatic conditions, among them drought and salt stress, photo-damage and freezing tolerance (Table 1). These involve complex pathways of interacting proteins elicited by signals attenuated or amplified by equally complex processes. Manipulation with single or multiple gene additions is difficult and greater knowledge of the complex control mechanisms is needed.

Gene technology offers at least as much promise to the product as to the vine. Basic quality factors, such as suitable colour and sugar development, are of generic importance to all segments of the wine industry and are currently targeted in grapevine molecular biology. Grapevine biotechnology, however, is in its infancy in this regard; significant efforts are underway to shed light on the processes required prior to targetting genes and manipulating biochemical pathways to produce novel and desirable products.

Obstacles to the commercialisation of genetically improved grapevine cultivars

Despite the interesting possibilities of the use of gene technology in the improvement of grapes and wine, there has yet to be a single transgenic grapevine variety used on a commercial scale. Producers, consumers and regulatory authorities all have their concerns, and much more knowledge of the complex peculiarities of the grapevine genome and improvements offered by genetic transformation technology is required to answer questions.

In most countries, the approval of genetically modified (GM) products and the release of genetically modified organisms (GMOs) requires a number of guarantees: (i) a complete definition of the DNA sequence introduced; (ii) the elimination of any sequence that is not indispensable for expression of the desired property; (iii) the absence of any selective advantage conferred on the transgenic organism that could allow it to become dominant in natural habitats; (iv) no danger to human health and/or the environment from the transformed DNA; and (v) a clear advantage to both the producer and the consumer.4

There is a growing consensus that risk is primarily a function of the characteristics of a product, rather than the use of genetic modification per se. Thus «substantial equivalence», equal safety compared to analogous conventional food and beverage products,4 should be demonstrated. This safety consideration is often considered sufficient.

Issues of intellectual property might also threaten the release of genetic improvements. Patents covering many of the tools and methods commonly used in genetic engineering may require formal agreements that could cause ownership disputes and serious impediment to the commercialisation process.

The claim is also made that patents on genetically engineered organisms confer an unfair advantage on certain producers;4 thus there is pressure to justify trade bans and technical barriers to free trade on the basis of «social interest».

The marketing of wine currently relies to a great extent on label integrity and product identity. In the most profitable market segments, the varietal name, the origin of production and the vintage are the key bits of information presented on the label. Genetically improved grapevines should not interfere with established varietal names and predictable wine styles, and an industry relying on a few select cultivars would be very hesitant to introduce new varietal names.2,5 The description and naming of transgenic grapevines will determine, to a large extent, their acceptance by grape growers, winemakers and consumers.5

Given the immense marketing value contained in some varietal names, there is an urgent need for consensus that GM grapevines are little different to grapevine clonal selections, which have been selected on the basis of beneficial, spontaneous genetic variations. In fact, when clonal selections are used, the identity might be known to the grapegrower but the wine is still marketed under the varietal, and not the clonal name. It is not yet clear, though, whether improved transgenic grapevines will be assigned a new varietal name or just a new clonal number.

These uncertainties complicate the wine industry’s evaluation of transgenic grapevines. And as a consequence of its strong identities and deep cultural roots, this industry is less receptive than others to technologies that promise revolutionary changes. There is a consequent fear that gene technology could accelerate the tendency to standardise wines, leading to loss of local identity, variety and uniqueness.

The successful application of recombinant DNA technology in the wine industry will depend on assuring the commercial users of transgenic grapevines that existing, desirable characteristics have not been damaged, that the requirements of legislation are met and that the engineered cultivar will be stable in practice, with suitable procedures for monitoring. If convinced, these producers would be in a strong position to develop a new niche market for «GM wine». Wine consumers attracted to such niche markets are usually well informed and very curious; therefore, GM wines produced by a limited number of interested producers would certainly attract widespread attention.

This technology holds a significant array of benefits, but it is essential that the consumer be educated if the fear of the unknown is to be removed. Scientists must consistently inform the public and remain open about experiments, research and products. Consumers must be reassured of first-class, transparent regulatory systems and should be persuaded by clear demonstrations of safety. Only then will they feel empowered to make informed decisions.



References

1 Sefc, K.M.: «Microsatellite markers for grapevine: a state of the art». In: Molecular Biology and Biotechnology of the Grapevine 2001 (Roubelakis – Angelakis, K.A:, ed.), Kluwer Academic Publishers; 433-464.

2 Colova-Tsolova, V. et al.: «Genetically engineered grape for disease and stress tolerance». In: Molecular Biology and Biotechnology of the Grapevine 2001 (Roubelakis – Angelakis, K.A:, ed.) Kluwer Academic Publishers; 411-432.

3 Kikkert, J.R. et al.: «Grapevine genetic engineering». In: Molecular Biology and Biotechnology of the Grapevine 2001 (Roubelakis – Angelakis, K.A:, ed.) Kluwer Academic Publishers; 393-410.

4 Pretorius, I.S.: «Tailoring wine yeasts for the new millenium: novel approaches to the ancient art of winemaking», Yeast 2000; 16: 675-729.

5 Vivier, M.A. i Pretorius, I.S.: «Genetic improvement of grapevine: tailoring grape varieties for the third millenium», S Afr J Enol Vitic 2000; 21: 5-26.

 


Table 1 Targets for genetic improvement of grapevine cultivars and rootstocks

Target traits

Target processes

Target genes and proteins

Disease resistance

 

 

Tolerance to fungal diseases

 

Defence signalling in response to fungal pathogens

Pathology of fungal pathogens

Innate resistance towards fungal pathogens

Glucanase and chitinase from fungi, yeast and plants

Ribosome inactivating proteins

Thaumatin-like protein (antifungal peptides from plants and insects)

Polygalacturonase- inhibiting proteins from plant species and stilbene phytoalexins

Phenylalanine ammonia lyase

CuZn superoxide dismutase

Detoxification enzymes

Tolerance to bacterial diseases

Defence signalling in response to bacterial pathogens

Pathology of bacterial pathogens

Innate resistance towards bacterial pathogens

Anti-microbial peptides

Disfunctional import and integration protein from Agrobacterium

Tolerance to viral diseases

Epidemiology and molecular biology of virus infections and vectors

Pathogen-derived resistance strategies

Virus coat proteins

Virus movement proteins

Replicase

Proteinases

Oligoadenylate synthase

Stress tolerance

 

 

Water stress

Aquaporins

Isolation of root-specific promoters

Tonoplast integral proteins

Plasma membrane integral proteins

Oxidative damage

Carotenoid biosynthesis and control

Anaerobiosis

Carotenoid biosynthesis factors

Alcohol dehydrogenase

Chloroplast and mitochondrial CuZn superoxide dismutase

Osmotic stress

Other abiotic stresses

Proline accumulation

Polyamines in stress

Freezing tolerance

Ornithine aminotransferase

Glycine betaine and antifreeze peptides from Antarctic fishes

Quality factors

 

 

Colour development

Ripening related signals and anthocyanin biosynthesis and control

Isolation of berry-specific promoters

Glucose:flavanoid glucosyltransferase and regulatory sequences

Production of pelargonidin-based anthocyanins

Anthocyanin methyl-transferases

Sugar accumulation and transport

Phloem loading and unloading

Sugar transport

Isolation of berry-specific promoters

Plant and yeast invertases

Hexose transporters

Reduced browning (table and dried grapes)

Oxidation reactions

Polyphenol oxidase (silencing)

Seedlessness (table grapes)

Seed formation

Baranase

[26.05.04]

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