International Journal Abstracts

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International Journal Abstracts

The following research results, of which the abstracts are provided here, have been published in various International Journals during 2006.

The grapevine polygalacturonase-inhibiting protein (VvPGIP1) reduces Botrytis cinerea susceptibility in transgenic tobacco and differentially inhibits fungal polygalacturonases
D.A. Joubert ¹, A.R. Slaughter ², G. Kemp ³, John V.W. Becker ¹, G.H. Krooshof ⁴, C. Bergmann ⁵, J. Benen ⁴, I.S. Pretorius ⁶ & M.A. Vivier ¹
¹ Department of Viticulture & Oenology, Institute for Wine Biotechnology, Stellenbosch University, Stellenbosch 7600, South Africa
² Department of Biochemistry, Institute of Botany, University of Neuchatel, Rue Emile-Argand 11, CH-2007 Neuchatel, Switzerland
³ Department of Plant Sciences, University of the Free State, Bloemfontein 9300, South Africa
⁴ Laboratory of Microbiology, Wageningen University, Wageningen 6703 HA, The Netherlands
⁵ Complex Carbohydrate Research Centre, University of Georgia, Athens, Georgia 30602-4712, USA
⁶ The Australian Wine Research Institute, Waite Road, Urrbrae, Adelaide, SA 5064, Australia
Abstract Polygalacturonase-inhibiting proteins (PGIPs) selectively inhibit polygalacturonases (PGs) secreted by invading plant pathogenic fungi. PGIPs display differential inhibition towards PGs from different fungi, also towards different isoforms of PGs originating from a specific pathogen. Recently, a PGIP-encoding gene from Vitis vinifera (Vvpgip1) was isolated and characterised. PGIP purified from grapevine was shown to inhibit crude polygalacturonase extracts from Botrytis cinerea, but this inhibitory activity has not yet been linked conclusively to the activity of the Vvpgip1 gene product. Here we use a transgenic over-expression approach to show that the PGIP encoded by the Vvpgip1 gene is active against PGs of B. cinerea and that over-expression of this gene in transgenic tobacco confers a reduced susceptibility to infection by this pathogen. A calculated reduction in disease susceptibility of 47 - 69% was observed for a homogeneous group of transgenic lines that was statistically clearly separated from untransformed control plants following infection with Botrytis over a 15-day-period. VvPGIP1 was subsequently purified from transgenic tobacco and used to study the specific inhibition profile of individual PGs from Botrytis and Aspergillus. The heterologously expressed and purified VvPGIP1 selectively inhibited PGs from both A. niger and B. cinerea, including BcPG1, a PG from B. cinerea that has previously been shown to be essential for virulence and symptom development. Altogether our data confirm the antifungal nature of the VvPGIP1, and the in vitro inhibition data suggest at least in part, that the VvPGIP1 contributed to the observed reduction in disease symptoms by inhibiting the macerating action of certain Botrytis PGs in planta. The ability to correlate inhibition profiles to individual PGs provides a more comprehensive analysis of PGIPs as antifungal genes with biotechnological potential, and adds to our understanding of the importance of PGIP:PG interactions during disease and symptom development in plants.
Transgenic Research 15 2006 687 - 702

The effect of increased branched-chain amino acid transaminase activity in yeast on the production of higher alcohols and on the flavour profiles of wine and distillates
M. Lilly ¹, F.F. Bauer ¹, G. Styger ¹, M.G. Lambrechts ² & I.S. Pretorius ¹,³
¹ Institute for Wine Biotechnology, Stellenbosch University, Victoria Street, Stellenbosch, South Africa
² Distell, Stellenbosch, South Africa
³ The Australian Wine Research Institute, Waite Road, Urrbrae, Adelaide, SA, Australia
In Saccharomyces cerevisiae, branched-chain amino acid transaminases (BCAAT ases) are encoded by the BAT1 and BAT2 genes. BCAATases catalyse the transfer of amino groups between those amino acids and ?-keto-acids. ?-Keto-acids are precursors for the biosynthesis of higher alcohols, which significantly influence the aroma and flavour of yeast-derived fermentation products. The objective of this study was to investigate the influence of BAT-gene expression on general yeast physiology, on aroma and flavour compound formation and on the sensory characteristics of wines and distillates. For this purpose, the genes were over-expressed and deleted in a laboratory strain, BY4742, and over-expressed in an industrial wine yeast strain, VIN13. The data show that, with the exception of a slow growth phenotype observed for the BAT1 deletion strain, the fermentation behaviour of the strains was unaffected by the modifications. The chemical and sensory analysis of fermentation products revealed a strong correction between BAT gene expression and the formation of many aroma compounds. The data suggest that the adjustment of BAT gene expression could play an important role in assisting winemakers in their endeavour to produce wines with specific flavour profiles.
FEMS Yeast Research 6 2006 726 - 743

The effect of increased yeast alcohol acetyltransferase and esterase activity on the flavour profiles of wine and distillates
M. Lilly ¹, F.F. Bauer ¹, M.G. Lambrechts ², J.H. Swiegers ³, D. Cozzolino ³ & I.S. Pretorius ³
¹ Institute for Wine Biotechnology, Stellenbosch University, Private Bag X1, Matieland, Stellenbosch 7600, South Africa ² Distell, PO Box 184, Stellenbosch, 7599, South Africa ³ The Australian Wine Research Institute, PO Box 197, Glen Osmond, Adelaide SA 5064, Australia
The fruity odours of wine are largely derived from the synthesis of esters and higher alcohols during yeast fermentation. The ATF1- and ATF2-encoded alcohol acetyltransferases of S. cerevisiae are responsible for the synthesis of ethyl acetate and isoamyl acetate esters, while the EHT1-encoded ethanol hexanoyl transferase is responsible for synthesizing ethyl caproate. However, esters such as these might be degraded by the IAH1-encoded esterase. The objectives of this study were: (a) to over-express the genes encoding ester-synthesizing and ester-degrading enzymes in wine yeast; (b) to prepare Colombard table wines and base wines for distillation using these modified strains; and (c) to analyse and compare the ester concentrations and aroma profiles of these wines and distillates. The over-expression of ATF1 significantly increased the concentrations of ethyl acetate, isoamyl acetate, 2-phenylethyl acetate and ethyl caproate, while the over-expression of ATF2 affected the concentrations of ethyl acetate and isoamyl acetate to a lesser degree. The over-expression of IAH1 resulted in a significant decrease in ethyl acetate, isoamyl acetate, hexyl acetate and 2-phenylethyl acetate. The over-expression of EHT1 resulted in a marked increase in ethyl caproate, ethyl caprylate and ethyl caprate. The flavour profile of the wines and distillates prepared using the modified strains were also significantly altered as indicated by formal sensory analysis. This study offers prospects for the development of wine yeast starter strains with optimized ester-producing capability that could assist winemakers in their effort to consistently produce wine and distillates such as brandy to definable flavour specifications and styles.
Yeast 23 2006 641 - 659

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