Abstract
Plants produce secondary chemicals to interact with and adapt to their environment. The plant flavonoid metabolic pathway is responsible for several different and important ecological roles, including pigmentation, UV radiation screening, stress amelioration and defense against herbivores and pathogens. The flavonoid pathway is an ideal model for exploring the evolution of biochemical and genetic networks because of its relatively simple biochemical basis and well-characterized phenotypic expression. To explain the flavonoid pathway, I used the widespread plant Silene vulgaris (“bladder campion”), which grows across several elevational gradients. I predicted that at high elevations, UV screening would be a constant necessity, so wanted to observe what would happen to plant pigmentation and defense against herbivores at high elevation plants as these traits are linked through shared flavonoid pathway enzymes. I also hypothesized that the flavonoid pathway would play a role in adaptation to the local environment.
First, I found that S. vulgaris expresses anthocyanins and at least 15 different flavones in its leaves, petals, and calyces, with significant differentiation among tissues. Plants also express signatures of their geographic origin, with calyces being the most distinct tissue. Second, I found evidence for divergence in the flavonoid pathway along elevational gradients in the French Alps. Plants at higher elevations had more darkly pigmented calyces and petals, and their leaves had higher levels of UV-screening flavones. I did not find evidence for any associations between flavonoid chemicals and herbivory. Third, naturally high- and low-elevation origin plants,reciprocally transplanted into high- and low-elevation gardens, had genetic and environmental influence to calyx color, whereas leaf flavone concentration and diversity was largely environmentally induced. Lastly, I measured flavonoid pathway gene expression in a subset of the reciprocal transplant individuals. Genes that were significantly different in expression were responsible for flavone production and glycosylating flavonoids (thus creating flavonoid diversity). Overall I was able to determine that the flavonoid pathway plays a role in adaptation to elevational environments through both natural selection and environmental inducibility.
