Temporal and carbon dependent patterns in gibberellin biosynthesis and growth

Plant growth shows rhythmic behaviour during day/night cycles and is highly dependent on environmental conditions. Gibberellin (GA) plays a key role in growth control. However, a lot remains unclear regarding how GAs interplay with light, sugar availability and the circadian clock, to ensure proper timing and magnitude of plant growth. Therefore, this study explores how these cues regulate GA biosynthesis. First, we identified GA biosynthetic genes that showed rhythmic transcriptional behaviour throughout the day-night cycle in adult Arabidopsis rosettes. Of these, KAURENE SYNTHASE (KS) was the only GA biosynthesis gene that retained rhythmicity under continuous light conditions. However, GA20OX1 and GA3OX1, the genes that encoded final enzymatic steps of GA biosynthesis required a shift to light or darkness respectively for their induction. We present data that supports a model of rhytmic GA biosynthesis where GA precursors are made during the day and converted to bioactive GA during the night in a resource, light and clock dependent way. This thesis highlights the importance of timing of growth and synchronization between external (day-night rhythm) and internal cues (circadian clock and sugar availability).