EXPRESSED PLANT NUCLEAR GENES IN THE SOLANACEAE: UNIFICATION OF PHYLOGENETIC INFERENCE WITH CHARACTER EVOLUTION

The Solanaceae is one of the most economically important plant families in the world because it contains tomato, potato, eggplant, peppers, and tobacco and produces a diversity of species with a wide range of floral morphologies. Because of its great importance, many studies have been directed towards producing evolutionary-based classifications of the family; however, additional investigations are required to corroborate previous findings. Evolutionary-based classifications are necessary because they provide valuable frameworks that can be used to predict species that may provide valuable chemicals that are medicinally important or traits that could be useful to crop breeders. The first objective of this project is to use cDNA sequences of the protein salicylic acid methyltransferase (SAMT) to test and refine existing evolutionary-based classifications of the tomato family. Shown in Figure 1 is a phylogenetic tree representing Solanaceae relationships that we have estimated with SAMT. The relationships shown are largely congruent with previous estimates using chloroplast sequence and RFLP data. In addition to resolving phylogeny, studies of the SAMT gene sequences have the potential to reveal how plants communicate with organisms in their environment. SAMT is critical for plant survival and reproduction because it makes a chemical (methyl salicylate; Figure 2) that is involved in pathogen and herbivore defense, and in addition, is produced by flowers as a scent compound for pollinator attraction. The ability to produce methyl salicylate as a floral scent compound has evolved multiple times in Solanaceae evolutionary history (Figure 3). Because multiple independent gains of character traits are hypothesized to be due to either parallel or convergent evolution, a second aim of this project is to test these two hypotheses. If orthologous rather than paralogous genes are involved in scent production in the independent lineages, this would support the hypothesis of parallel, rather than convergent evolution of methyl salicylate production. Because of the multiple important roles this protein plays in the tomato family, the third objective of this project is to characterize SAMT expression patterns in leaves and flowers to determine how plants have evolved the ability to manipulate the regulation of this protein for these distinct functions. To do this we will assay for SAMT gene upregulation in various tissues and in response to various treatments to begin to understand how gene expression has evolved in this family. Overall, this study combines gene sequence data with gene expression data to provide an avenue into understanding how plants have evolved to defend themselves against pathogens and herbivores but at the same time attract insects for pollination.