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A Technical Guide for Wine Producers
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Fine-tuning grape ripening: superior wine through genetic control
Mauritz Venter1
1 Department of Genetics, Stellenbosch University, P/Bag X1, Matieland, 7602, South Africa
"Times are changing." These words are hard to accept when old and established rules still dominate the wine-makers playground. It is all about perception. Even where age-old traditions exist, the unprecedented advance of grapevine biotechnology has yielded a myriad of new biological data and technologies, impossible to ignore. The use of genetic enhancement strategies: to "design" that ultimate cultivar, protected against all the elements, will only take time (and maybe a few "heavy-weights" in the business) for perceptions to change! In this biotech revolution, it may seem that grapevine research have a ‘less important’ role to play when compared to "hot-shot" science dealing with cancer or stem cells! However, conducting research in a valley where most of the fertile ground harbours a special fruit and trying to discover intricacies regarding all elements responsible for good wine, make grapevine an exciting model to study and manipulate.
Successful genetic manipulation of grapevine requires useful genes to confer specific traits and suitable molecular "switches" known as promoters that control the site and level of gene activity in certain tissues, during different stages of development and/or in response to different elements or conditions. Focussing specifically on promoters, all creatures, plants and organisms have these regulatory elements in their genetic make-up. Every promoter contains a combination of different ‘sensors’ and these sensors, known as regulatory motifs, are the key players responsible to activate the promoter in response to conditions such as temperature fluctuations, drought stress, ripening signals, pathogen attack, wounding etc. In grapevine, the target-genes regulated by these promoters can be responsible for various cues influencing the quality and stability of good wine. Certain genes have been well characterised and are directly associated with factors such as sugar-acid metabolism, cell wall metabolism, wine aroma as well as disease and environmental stress tolerance. Analyses of ripening-related genes and the subsequent isolation of promoters in a seasonal crop like grapevine can be a daunting task and therefore, necessitates the implementation of cutting edge research, new technologies and innovative ideas. Scientists today are able to "cut and paste" different segments of DNA to achieve a desired trait. Combined with a well established system to evaluate and use promoter elements in grapevine (and other plants), the possibilities should be endless (Figure 1). However, from theory to practice, promoters implemented to address potential concerns and/or needs that the wine farmer might have, is not so straightforward!
Understanding the complex nature of grapevine molecular biology is of great importance for viticulturists and this is no "pie in the sky" research effort. In theory, this information can be used to design and produce tailor-made promoters for the wine farmer’s needs. However, evaluation of "foreign" genetic elements in plants is an expensive and time-consuming process. Therefore, it is necessary to use bioinformatics (where the biologist meets the computer scientist) to formulate putative predictions on how such a molecular switch might behave in the grape berry in response to specific cues. The bioinformatics approach is useful but it is necessary to emphasize that predictions
to understand how a promoter could function must ultimately anticipate experimental confirmation. The combination of promoter and target gene (regulated by that particular promoter) in response to e.g. hormone treatment, different sugars levels, pH fluctuations and/or various stress conditions (heat and cold shock) plays a crucial role in a genetic engineering program.
Realistically, we can only imagine that the use of a genetically modified grape to be used in the production of a very special and expensive bottle of red, will be strangely looked upon by any wine "master" or "connoisseur". The time frame for commercial release of genetically improved grapevine plants is predicted to be between 5 to 10 years. It is realized that due to the long seasonal growth cycle and regeneration time of grapevine during transformation, the evaluation of molecular ‘tools’ such as promoter elements in stable transformed plants bearing fruit will be time-consuming. That is the nature of applied biological research. However, biotechnology has allowed us to combine modern genetics and conventional breeding strategies to produce a grape berry that could be engineered for stress and disease tolerance. And additionally be improved to potentially meet the exact requirements of the wine farmer regarding elements to make good wine. Therefore, successful genetic improvement and the subsequent commercial release of grapevine will depend on accomplishing a collaborative effort between scientists, wine farmers and a change in public perception.
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