Biotechnol. J. 2008, 3, 1355–1367
al tolerance and inhibition of protein translation are also known. The unique genetic resources ob- tained in this study have entered our biotechnolo- gy programme where improved disease resistance of grapevine is the main aim.
The utility of single genes encoding specific proteins, PGIP or antifungal peptides, with marked anti-fungal activity genetically engineered into grapevine is an extremely useful technology for the control of vineyard pathogens [2, 7]. Further re- search aimed at understanding the dynamics of plant-pathogen interactions and the role of pro- teins with antifungal activity will offer better in- sights into the potential of utilising this technology in plant protection strategies.
Apart from the common biotic threats, viruses, fungi and insects, grapevine plants are susceptible to abiotic stresses caused by environmental change. One common type of abiotic stress found in South Africa is drought. Southern Africa is facing progressively worsening water shortages with the result that crop productivity suffers, thus negative- ly influencing the regional economy. Grapevine is no exception where water stress can significantly impact factors such as canopy growth and bunch quality. Water stress also effects properties such as photosynthetic efficiency and can promote photo- oxidative stress resulting in reactive oxygen species (ROS) production. To develop grapevines with enhanced capabilities to grow under adverse conditions, in particular water stress, the IWBT grapevine programme is utilising genetic resources developed by studying the carotenoid biosynthetic pathway in grapevine. This pathway produces metabolites or compounds involved in environ- mental stress responses (antioxidant molecules), quality parameters of grapes (aroma molecules) and the formation of the stress hormones (such as abscisic acid). The understanding and manipula- tion of carotenoid metabolism in grapevine will provide insight into how grapevine deals with abi- otic stresses, but can also provide alternative strategies to counteract, and/or produce novel plant material more resistant, to these stresses. Moreover, the work also aims to contribute towards a fully characterized vineyard where the cause(s) and effects of environmental stresses can be sepa- rated and studied.The metabolic pathways that will be studied are also intricately involved in quality aspects and so some of the research objectives re- late to functional analysis of impact genes and their encoded products to improve flavour and aroma production in grapevine tissues and berries.
Carotenoids play a central role in plant metab- olism in general, and specifically in photosynthesis where they perform a myriad of functions. In addi-
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tion to being integral structural and accessory light-harvesting components of the photosynthetic apparatus, their ability to quench ROS formed un- der adverse conditions, thereby protecting the pho- tosynthetic machinery against damage, is invalu- able. Carotenoids also serve as important precur- sors for apocarotenoids. These apocarotenoids or norisoprenoids are involved in a wide range of functions in plants and can be growth regulators, pigments, flavours and aromas. Abscisic acid is an important apocaroteniod involved in growth regu- lation and stress responses. Norisoprenoids are frequently aromatic and volatile in nature and con- tribute to the varietal character of a number of im- portant cultivars while having very low odour de- tection thresholds.
Work in the grapevine programme has lead to the cloning and characterisation of most of the genes encoding enzymes involved in the pathway [13–16]. The role of these enzymes have been as- sessed in further studies by overexpression of se- lected genes in tobacco and Arabidopsis . The resultant transgenic plants have been assessed genotypically and phenotypically characterised to provide us with insights into the functional role of these genes in plants. These analyses revealed a number of parameters involved or affected during drought tolerance. Collectively, these results con- firm and advance our existing knowledge of the role of carotenoid biosynthesis in drought toler- ance and the specific mechanisms operating on a whole plant level.
A clear understanding of the respective genes, proteins and enzymes that contribute to the carotenoid biosynthetic pathway is needed to suc- cessfully apply genetic manipulation strategies. To support this research, a grape berry tissue culture system is being developed.The aim is to determine whether such a system would be suitable as model system to investigate berry ripening and other berry-specific processes. In summary, the current projects focus on improving our understanding of genetic networks and mechanisms responsible for the plant’s response to biotic and abiotic (environ- mental) stresses, as well as the aroma and flavour development in grape berries and the regulation thereof. Systems biology tools are increasingly im- plemented into the programme as they become available.
The datasets generated will also allow careful evaluation of current manipulation strategies and support the development of improved approaches in the future.