Biotechnol. J. 2008, 3, 1355–1367
PGIP-encoding gene from grapevine (Vvpgip1) is no exception [10, 11]. When expressed in a model plant system such as tobacco, the protein confers a clear advantage to plants challenged with B. cinerea, leading to significant improvements in dis- ease resistance [10, 11]. The mechanisms by which PGIP confers reduced disease susceptibility against B. cinerea and fungal pathogens are not ful- ly understood. One mechanism thought to be in- volved is through the direct inhibition of cell wall maceration enzymes secreted by fungal pathogens [10, 11]. The disease protection can be clearly ob- served by comparing tobacco plants overexpress- ing a potent endopolygalacturonase (endoPG) from Botrytis, leading to severe tissue maceration and plant structural collapse, whereas plants co- expressing both the endoPG and the PGIP display a far less severe phenotype [10, 11]. Experimental evidence also suggests that PGIPs could have func- tions totally unrelated to their activity, but still im- portant for plant defence . Tobacco lines har- bouring the grapevine PGIP have been shown to have an up-regulated disease resistance as well as significantly more lignin than untransformed con- trols (unpublished observations). This wall-associ- ated phenotype is also reflected on a transcription- al level and genes involved in cell wall biosynthe- sis and structural organisation in transgenic tobacco over-expressing PGIP (unpublished ob- servations). These results have spurred further re- search into identifying the nature of the direct and indirect mechanisms that may be responsible for
these disease resistance phenotypes. Numerous PGIP genes have been cloned and sequenced from V. vinifera as well as wild Vitis species and are cur- rently being investigated for improved resistance activity.
Similarly, the first antifungal peptides from grapevine (VvAMP1) have been cloned. Purified peptide has been tested against economically im- portant grapevine pathogens, showing significant activity against several of them . Antifungal peptides are believed to mediate their activity through targeting the membrane structures of in- vading fungal organisms leading to pathogen death. The exact mechanisms, in a similar vein to the PGIP mode of action, appear to be the result of direct and indirect action on cellular processes.An- tifungal plant peptides and their encoding genes are abundant in most plant species and have a rec- ognized biotechnological potential in both the medical and agricultural biotechnology sectors. These peptides typically contribute to preformed defence by developing protective barriers around germinating seeds or between different tissue lay- ers within plant organs.
South Africa has a rich and unique floral biodi- versity and some native Brassicaceae spp. were tar- geted for the potential isolation of additional novel antifungal peptides. Fourteen new plant defensin sequences from four genera of the Brassicaceae family present in South Africa were isolated. Mem- bers of this group are well known for their strong antifungal activity, but other activities such as met-
YEAST BIOTECHNOLOGY Extracellular enzymes to improve processing and wine quality
STA1/DEX2/MAL5, EXG1/BGL1, BGL2, SSG1/SPR1, EXG2, PAD1/POF1, CTS1-2, PEP4, ATF1/IAH2, PGU1/PGL1, STA2/DEX1, STA3/DEX3, SGA1, LKA1, LKA2, S FA1, SFG1, RSA1, RSG1, XYS1, XYN2, XYNC, XYN5, BGLA, XYL1.
Modified adhesion properties (flocculation, sedimentation and turbidity in wine)
MSS10, MSS11, FLO1, FLO5, FLO8, FLO10, FLO11/MUC1, CLN1, CLN2, GPA2, ASH1, STE7, STE11, STE12, TEC1, MSN1, NRG2, ROM1, ROM2, SOK2, KSS1, PH D1, RAS2, RME1, SCH9.
Aroma compound metabolism (improved sensory qualities) CAT2, YAT1, YAT2, CIT2, AGP2, ATF1, ATF2, BAT1, BAT2, GPD1, GPD2 , AAT10, AAT11.
GRAPEVINE BIOTECHNOLOGY Increased isoprenoid levels/general metabolism (multiple metabolic functions)
Mevalonate pathway: VvAACT, VvHMGS, VvHMGR, VvMK, Deoxyxylulose 5-diposphate pathway: VvDXS , VvDXR , VvispE, VvispF, VvispG, VvispH, General: VvIPI, VvFPS, VvGPS, VvGGPS.
Increased abiotic stress tolerance (drought, light) and/or fruit quality (flavour, aroma)
Carotenoid biosynthetic pathway: VvPSY , VvPDS , VvZDS, VvCiso, VvLECY , VvECH , VvLBCY, VvBCH, VvZEP , VvVDE , VvNSY . Abscisic acid biosynthetic pathway: VvNCED , VvCCD.
Antifungal/disease resistance (against bacterial, fungal and insect pests)
Polygalacturonse-inhibiting proteins: Vvpgip1, 38 pgip genes from Vitaceae and Muscadinia. Antifungal peptides: Vv-AMP1, MiAFP1-MiAFP3, HcAFP1-HcAFP6, LaAFP1-La-AFP4,
LmAFP1-Lm-AFP2. General defense genes: vst1, Ntcad, CST1-2, EXG1.
Figure 2. Examples of genes isolated in the IWBT yeast and grapevine biotechnology pro- grammes in the last 10 years.