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R.J. Griesbach and R.M. Beck

The sequence of the intron within the chalcone synthase A gene (ChsA) was used to characterize Petunia integrifolia subsp. integrifolia var. depauperata (Fries) Smith et Downs, P. altiplana Ando et Hashimoto, P. littoralis Smith et Downs, and an unknown taxon from the town of Torres in Brazil. Based upon the intron, the Torres taxon most closely resembled P. integrifolia. The unrooted phylogenetic tree suggested that P. integrifolia was more closely related to P. littoralis than P. altiplana.

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R.J. Griesbach, R.M. Beck and J.R. Stehmann

A method was developed to characterize the genetic heterogeneity of the chalcone synthase gene intron within the Petunia integrifolia (Hook.) Schinz & Thell. species complex. The DNA from wild species collected from known locations was used to amplify the chalcone synthase gene intron through the polymerase chain reaction (PCR). The resulting PCR product was then characterized by Rsa 1 restriction, revealing a degree of heterogeneity that could be used to characterize the species genetically. Of the four different species that were characterized, two could be placed in the same genetic grouping. This study shows that the variation in the intron of the Chs A gene may be species-specific.

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Robert J. Griesbach, Ronald M. Beck, John Hammond and John R. Stommel

Gene silencing is one of the ways in which gene expression is controlled. The authors have developed a model system to study anthocyanin gene silencing using a recessive mutation in Petunia Juss. (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).