Technical Abstract: Differences in structural gene expression are responsible for a wide range of responses from human cancer to patterned flowers. Gene silencing is one of the ways in which gene expression is controlled. We have developed a model system to study anthocyanin gene silencing using a mutation in Petunia (Star mutation) and the ability of certain viruses to reverse the gene silencing mutation. In healthy plants, the star pattern was enhanced (increase in level of gene silencing) under high temperature or light growing conditions. Virus-infection did not significantly influence the star pattern when plants were grown under either low light or low temperature conditions. Under high light and temperature conditions, virus infection reverses silencing leading to a change in the star pattern. These changes in the star pattern corresponded to changes in gene expression. Viral infection had a greater affect on regulatory gene (Wd40, Myc and Myb) expression than on structural gene expression (Chs and Ans).