In the life cycle of Arabidopsis thaliana and many other species, two developmental switches determine overall life history and consequent population biology: the switch to germination and the switch to flowering. Much is known about genes associated with adaptation in flowering time, molecular genetic pathways of flowering, and geographic distribution of natural variation in flowering time. Comparable effort devoted to understanding germination timing has the potential to provide significant insight into adaptation of entire life history schedules and the genetic basis of population variation. This research therefore focuses on the genetic basis and evolutionary ecology of germination timing. It has recently been found that the gene family of photoreceptors, the phytochromes, have important functions during germination that may give them the ability to regulate the season of germination. New data indicate that phytochromes are involved in both germination and its opposite trait: dormancy. Moreover, contributions of different phytochromes to germination depend on temperature. This research will test whether phytochrome can regulate the temperature of germination through mutant studies, compare gene expression in different phytochrome mutants, and test whether natural variation in germination involves variation in the expression of these same pathways. A geographic analysis of natural variation in germination responses will test for evidence of natural selection on germination on a regional scale. In addition to testing fundamental mechanisms of phytochrome regulation of germination, the proposed research will test for natural variation in the germination pathways regulated by phytochromes and test whether that natural variation is due to variation in expression of phytochrome-regulated genes or due to variation in phytochrome sequence itself. These studies of the genetic basis of germination responses and the geographic distribution of variation in germination will contribute significantly to our understanding of processes of range expansion and distributional changes accompanying environmental change. By combining modeling of flowering time and germination phenology, the goal is to predict life history and demography as a function of changing environmental conditions. Results of the phenotypic survey and microarray studies will be made available to the community and provide a foundation for future studies of the genetic basis of natural variation in germination. This research also supports international collaboration and training at various levels in genomic, physiological, and computational techniques.
