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item Hunter, Wayne

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2005
Publication Date: 1/1/2006
Citation: Huang, H., Lu, J., Hunter, W.B. 2006. Comparative sequence and functional analysis of stilbene synthase genes among vitis species. Acta Horticulturae.

Interpretive Summary: A set of stilbene synthase genes were identified from Vitis shuttleworthii, a grape with high levels of disease and insect resistance. These genes are related to a family of genes, referred to as the phytoalexins. The phytoalexins have critical functions in the protection of plants to many stresses, such as chemical or ultra-violet irradiation, and biotic-stresses, such as fungi, bacteria, viruses, and other infections. The severe impact of Pierce’s Disease, a bacterial pathogen, upon the U.S. grape industry has generated the need to rapidly understand disease resistance in grapes. Fungal and bacterial diseases prevent increasing grape production throughout most of the southeastern USA, especially in Florida where there is significant amounts of annual rainfall. Researchers have therefore turned to North American grapes which have naturally evolved to grow and thrive under these conditions. A grape species with promise is V. shuttleworthii. We selected this grape due to its natural resistance to diseases and insects, and it is currently being used in a grape breeding program at Florida A&M, in the production of new grape cultivars. To identify and isolate genes linked to disease resistance, scientists isolated a set of genes from a V. shuttleworthii. Leaf and flower tissues were used to produce a genetic library. The expressed sequence tags, ESTs, of these genes were then used to conduct comparative analysis to other known plant genes. After screening a set of 5,766 genes from V. shuttleworthii, comparative analysis identify 16 genes of interest. Stilbene synthase genes were identified, and are important antimicrobial compounds which function in the plant's defense system. Researchers are now trying to use this gene to increase disease resistance in other varieties (wine, raisin, table grapes) and species of grapes. Disease resistance strategies such as this will enable grape producers to use fewer chemicals on their crops.

Technical Abstract: Pierce disease (PD), anthracnose and downy mildew are the limiting factors in the production of European grapes (V. vinifera) in the southeastern United States, especially in Florida where annual precipitation is high. Native American grape species such as V. shuttleworthii, V. aestivalis and V. rotundifolia have evolved strong resistance to these diseases. In order to understand the genetic variation and expression of stilbene synthase, StSy, a phytoalexin, in grape species/varieties and their correlation to disease resistance, 32 sequences of the StSy among grape Vitis species were compared and analyzed. The StSy transcripts from V. shuttleworthii were also analyzed by BLAST comparison against 260 known StSy genes from plants retrieved from NCBI; this list included StSy identified as either full-length or partial sequences. Two V. shuttleworthii, StSy transcripts were represented in low abundance in both V. vinifera and V. shuttleworthii cDNA libraries. Interestingly, one of the StSy contigs was found to have significantly higher transcriptional, expressed sequence tag (EST) abundance in the V. shuttleworthii library while being less represented in the V. vinifera libraries. While differences may be in part to variation in library construction or plant biology when samples were taken examine the differential StSy expression of these three transcripts during challenge by disease pathogens there appeared to be a correlation. Homologous relationships among the StSy multigene family were analyzed by multiple alignments of protein sequences (BLASTP and PAUP). Single nucleotide polymorphism (SNP) sites in the coding region were discovered within the multigene family. Amino acid analyses showed that some of the single nucleotide substitution resulted in amino acid changes. Correlations between single nucleotide substitutions /amino acid changes and disease resistant phenotypes were identified. Analysis of the cSNPs among the StSy appears to be a useful approach for identification of disease resistance in grape phenotypes and is being further evaluated for application to screen current and newly selected grape cultivars for increased disease resistance.