Pigliucci 9707552 Molecular geneticists and physiologists working with the model system Arabidopsis thaliana have achieved a detailed mechanistic understanding of two distinct forms of phenotypic plasticity: the response to light quality and the response to photoperiod. These analyses have clearly established that there is extensive overlap among the genes that regulate these two forms of plasticity, raising questions about the evolutionary origins and ecological implications of pleiotropy and genetic redundancy. The PIs' understanding of these genetic details allows us to address a complex question: how do plants integrate a suite of cues that provide information about different aspects of multifactor selective environments? For annual plants, light quality serves as a specific and reliable cue for present and imminent competition for light, because encroaching competitors alter light quality (i.e., the ratio of red to far-red light - R:FR). Similarly, in the temperate regions where A. thaliana grows, the length of the photoperiod is an indicator of seasonality. Can natural populations of A. thaliana respond to selection on the ability to sense and respond to light quality cues? How strong is the relationship, if any, between the R:FR-mediatedplasticity syndrome, andphotoperiod-mediated plasticity? The PIs will propose a short-term selection experiment with replicated selection and control lines. The PIs will work with a large natural population already under intensive study in East Tennessee. We will select directly on the R:FR-mediated plasticity of flowering time. While assessing the response to this direct selection, we will also examine two forms of indirect response. First, was there a response in the R:FR-mediated plasticity of other traits? Second, was there a response in the photoperiod-mediated plasticity (i.e., a different cue) of the same trait, flowering time? The PIs' plan to address the interaction among traits and be tween R:FR- and photoperiodmediated plasticity in a series of mutant lines. These mutants lack specific photoreceptor genes that affect a suite of traits, including reproductive fitness. Furthermore, in these mutant lines and their associated wild types, normal and altered patterns of plasticity occur in the same genetic background. Thus, it is possible to make strong inferences about how a gene (or genes) controlling plasticity affects the whole organism, including its performance or fitness (pleiotropy).
