Determining day length and temperature regulation of flowering: a molecular and modelling approach

Thesis (Ph.D.)--University of Washington, 2016-08

In nature, plants are exposed to numerous abiotic and biotic pressures. Temperature, day length, light quality, length of winter, herbivors, nutrients, and pathogens all affect plant development and change throughout the growing season. Plants have evolved to act proactively or reflexively to mitigate negative effects and to time their development to favorable times of the year. The molecular mechanisms for many of these pressures in isolation are well understood; however, we do not yet understand how plants may perceive and integrate multiple environmental factors at once. In light of climate change, understanding plant responses in natural settings is especially crucial. Here, I review how the molecular pathways controlling the circadian clock interact with pathways involved in perceiving environmental cues to modulate circadian-regulated phenomena such as flowering, diurnal leaf growth, and the cold response. I discuss how several pathways converge to regulate a few key genes, and that this may be how plants are able to integrate multiple environmental pressures. I, then, explore the molecular responses of two key flowering genes – FLOWERING LOCUS T (FT) and CONSTANS – to assess the combined influence of day length changes and temperature cycles on flowering. I show that cool temperatures can both suppress and induce FT, and that FT levels are highly predictive of flowering across a range conditions. Next, I incorporate these mechanisms into an existing model, which already included day length regulation of FT and temperature regulation of leaf tissue production. I show that incorporating the mechanisms of temperature regulation on FT coupled with accumulating FT with increasing leaf tissue as the plant grows can improve model predictions in fluctuating temperature environments. I discuss how such an approach might be used to improve the predictions of crop models. Finally, I discuss questions that still remain and provide recommendations for future study.