The role of phyB in the control of reproductive timing.

This BBSRC project (P19861) sought to understand the role of the light receptor phyB in regulating flowering time and other physiological responses.

Flowering time is regulated by photoperiod sensors such as phyB. The prevalent hypothesis is that day length perception is mediated through coupling of an endogenous rhythm with an external light signal. In Arabidopsis, the clock-regulated genes CONSTANS (CO) and FLAVIN, KELCH, F-BOX (FKF1) and their light-sensitive proteins are thought to form an external coincidence sensor. We modelled the integration of light and timing information by CO, its target gene FLOWERING LOCUS T (FT), and the circadian clock (Salazar et al. Cell 2009). Our models showed that FKF1 activates FT. We demonstrated experimentally that this effect is independent of the known activation of CO by FKF1, locating a major, novel controller of photoperiodism.

This project also examined the connections between the phyB light receptor and auxin, a transmissible hormone that regulates growth and plant architecture. In this study, we showed that phyB regulates the emergence of lateral roots, at least partly by manipulating auxin distribution within the seedling (Salisbury et al., Plant J. 2007). Thus, shoot-localized phytochrome is able to act over long distances, through manipulation of auxin, to regulate root development. This work revealed an important role for phytochrome as a coordinator of shoot and root development, and provided insights into how phytochrome is able to exert such a powerful effect on growth and development.

1. The incorporation of modelling approaches which we were able to do through collaboration, illustrated the power of models in solving complex problems and generating predictions that would not have been possible through experimentation alone. We used modelling to define and explain the dynamics of the molecular circuitry that regulates flowering time in Arabidopsis. Model-led predictions uncovered a novel role for the clock-associated protein FKF1 in photoperiodic flowering.

2. We demonstrated that the light receptor phyB coordinated shoot and root growth through the transmissible hormone auxin. In this way we showed that phyB located in the seedling leaf could imposed control on distant organs such as the root.