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Robert Griesbach* and Ronald Beck

The genetic distance for three Petunia species was determined based upon an intron in the chalcone synthase gene. The sequence of the intron was obtained for P. integriflolia ssp. integriflolia var. depauperata, P. integriflolia ssp. integriflolia Torres ecotype, P. altiplana and P. littoralis. These species are very closely related and believed by some taxonomists to be part of a large single species complex. In all the taxa, the intron contained multiple repeated and inverted sequences. The P. integriflolia ssp. integriflolia Torres ecotype intron differed from the P. integriflolia subsp. integriflolia var. depauperata intron in 3 of 930 nucleotides. While, the P. littoralis intron differed from the P. integrifolia subsp. integrifolia var. depauperata intron in 15 of 930 nucleotides. As compared to the P. integrifolia subsp. integriflolia var. depauperata intron, the intron in P. altiplana intron was longer (1125 bp), had a section of 338 nucleotides with a completely different sequence, and differed by 27 of 787 nucleotides in the common sequence.

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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).