Light and circadian clock team up to control plant development
Light and the circadian clock control the timing of growth and neighbour sensing, and are critical for proper regulation of fitness and biomass. Linking these two pathways are the phytochrome-interacting factor (PIF) transcription factors. Despite a thorough knowledge of both pathways, details of their downstream effectors are poorly understood. With EU funding, the S6KDIURNALGROWTHARAB project obtained new insights on how the Arabidopsis 40S ribosomal protein S6 kinase (S6K), is regulated by the circadian clock. S6K is a TOR (Target of Rapamycin) target and a regulator of protein synthesis. Moreover, Arabidopsis thaliana S6K is regulated by nutrient availability, osmotic stress, phytohormone signalling (e.g. auxin) as well as sugar. Previous research by project members indicates that S6K is a good candidate for a molecular switch between cell growth and proliferation. S6K inhibits cell proliferation by association with a the RBR-E2F pathway but one of its genes, S6K1 is co-expressed with a crucial component of the circadian clock core oscillator. As S6K is encoded by two genes, S6K1 and S6K2, the researchers investigated the circadian regulation of Arabidopsis S6K1 and S6K2 at the transcriptional, translational and post-translational levels. Project research results indicated that the circadian clock provides additional transcriptional and post-translational regulation of S6Ks. Researchers tracked S6K1 and S6K2 expression patterns in different plant organs with specific developmental programmes. Specifically, they analysed hypocotyls, cotyledons and roots. They also evaluated how light, circadian and growth-related phenotypes associated with modulation of S6K transcript and protein levels. The added layer of transcriptional control is organ-specific, suggesting that S6K protein function could be adjusted to specific plant developmental programmes. The newly identified factors affecting circadian regulation of plant growth and development have the potential to transform plant-breeding programmes. These findings provide a new framework to understand how plant growth responses can be adjusted to different environmental conditions. This is of particular relevance considering the challenges that climate change will impinge on world crops.
Keywords
Light, circadian clock, plant growth, S6KDIURNALGROWTHARAB, S6K
