New Members of the Stilbene Synthase Gene Family from the Vitis aestivalis-Derived Grape Cultivar Norton

Abstract

Genomic clones of three different stilbene synthase genes were obtained from the Vitis aestivalis Michx.-derived disease-resistant grape cultivar Norton. Cloning was accomplished by using polymerase chain reaction with oligonucleotide primers specific to conserved stilbene synthase DNA sequences from Vitis and other plant genera. The coding region of each gene specified an amino acid sequence that was 91 to 98% identical to those encoded by various members of the stilbene synthase gene family in other grapevine species. Based on intron sequence homology and length, the cv. Norton genes fell in two distinct categories: one, represented by gene st3, was characterized by an intron of 136 bp, whereas the other, represented by genes st1 and st2, was characterized by a considerably longer intron that was only distantly related to the st3 intron. This is the second report on the identification of two different types of stilbene synthase genes from a grapevine genome, suggesting that these genes are represented by at least two subfamilies in Vitis. Comparison of the 5'-flanking sequences of st2 and the Vitis vinifera L. stilbene synthase gene Vst1 revealed extensive regions of homology interrupted by a 15-bp and a 28-bp stretch of DNA that were present in st2 but were absent at the corresponding positions in Vst1. One of these st2-specific sequences mapped within an area that was homologous to the pathogen-inducibility region of the of Vst1 promoter, whereas the other was located 40 bp upstream of the putative TATA box. In addition to the three genes that specified potentially functional stilbene synthase enzymes, a putative stilbene synthase pseudogene containing a frame-shift mutation was also cloned.