Light signalling networks in plant development

CASAL, JORGE J.

Perth

Conferencia; ComBio 2013; 2013

In addition to its role in photosynthesis, light affects plant growth and development as a signal. The light environment perceived by specific photoreceptors including phytochrome, cryptochrome, phototropin and UVR8 provides information that helps plants to adjust their body form and function to the prevailing conditions. When dark-grown seedlings become exposed to light, the photoreceptors reduce the activity of the E3 ligase CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1). I darkness, COP1 targets selected transcription factors required for photomorphogenesis to degradation. Light releases these targets from the negative regulation imposed by COP1, their pools build up allowing the progress of photomorphogenesis. In addition, upon light exposure active phytochromes migrate to the nucleus, where they bind the bHLH transcription factors PHYTOCHROME INTERACTING FACTORS (PIFs). PIFs are repressors of photomorphogenesis and phytochrome binding reduces their activity by causing their degradation in the proteasome and/or by reducing their binding to DNA targets. When light-grown plants are exposed to shade, photoreceptor activity is reduced, PIF activity is increased and the plant acquires a more competitive body form. One of the current hypotheses is that the responses to shade are also caused by increased COP1 activity. These short pathways between light signals and changes in expression of target genes describe a rather simple scenario but the key players are profusely connected to regulatory loops. This creates a rather intricate signalling network with links to the circadian clock, hormone signalling, defences, temperature signalling, etc. We are beginning to learn the functional dynamics of these multiple connections.