Circadian clock regulation of chemical communication between plants and pollinators: a case study of Petunia flowers and Manduca hawkmoths

Abstract

Pollination services from animals ensure successful reproduction and outcrossing for many flowering plants. Recruitment of pollinators most often involves a combination of signals which are deployed from floral tissues. The shape of a flower, its color, smell, opening time, nectar secretion, floral angle, and other factors have evolved in a variety of ways to attract pollinators, while also restricting visitation from unsuitable guests. In particular, floral scent is a “double-edged sword” which can allow for long-distance recruitment of pollinators, while potentially risking the attention of herbivores and ineffective pollinators. A daily rhythm of advertisement may help to ensure that only the most efficient pollinators are recruited, while mitigating advertisement to potential predators. In Chapter 1, I begin by reviewing the behavioral, physiological, and molecular evidence for circadian rhythms in floral scent emission. I cover the early empirical observations of floral scent rhythms, and discuss the progress of the field after technological advances in chemical analysis and molecular biology. In Chapter 2, I then investigate the molecular mechanism regulating floral scent emission in the nocturnally fragrant Petunia hybrida. I show that the clock component LATE ELONGATED HYPOCOTYL (LHY) directly represses the expression of ODORANT1 (ODO1) and other scent-related genes during the morning, restricting their expression to the evening: which leads to the emission of scent during the night. Chapter 3 then investigates the importance of the circadian clock to P. axillaris floral visitation by the nocturnally active hawkmoth Manduca sexta. I show that manipulation of the plant clock allows for disruption of floral visitation. I also show that M. sexta’s ability to sense and respond to floral scent signals is clock-regulated but light-repressed. In addition, male hawkmoths show a time-dependent sensitivity and responsiveness to floral scent. Finally, I give a summary of the research topics here considering recent advances in the field and specific areas requiring further study.