Clock-mediated control of gibberellin responses in Arabidopsis.

ARANA, MV; MARÍN, N; MALOOF, J; ALABADÍ, D; BLÁZQUEZ, MA

Valencia

Congreso; XVII Congress of the Federation of European Societies of Plant Biologist; 2010

Federation of European Societies of Plant Biologist

The circadian clock acts as central coordinator of plant activity, and it regulates key traits for plant fitness such as seed germination, gas exchange, flowering and growth.  Particularly, growth of germinating seedlings is restricted to certain times of the day, showing a maximum rate near dawn.  This pattern can be explained by the light-mediated degradation of PIF proteins during the day combined with the clock-mediated repression of PIF transcript accumulation early in the night.  This combined action yields high levels of PIF proteins at the end of the night, which are responsible for growth.  In addition to this mechanism, growth is controlled by several plant hormones such as gibberellins (GA), auxins and brassinosteroids, and GA action has been shown to involve the relief of the DELLA-mediated inhibition of PIF transcriptional activity.  Although GA signaling has been thoroughly studied in constant environments its contribution to plant growth under predictable daily environmental changes such as day/night cycles is still unknown.  Here we show that the circadian clock gates hypocotyl GA sensitivity, resulting in the promotion of GA signaling late in the night, the moment when maximum growth occurs.  This effect involves the transcriptional control of the GA receptors and influences both the daily patterns of DELLA accumulation and the rate of hypocotyl elongation.  Taken together, our results show that anticipation of biological events to external day and night cycles requires a functional GA signaling, and that the GA pathway is a relevant clock output for the control early plant developmental traits, such as daily growth rhythms.