“When we began our research, we knew plants had internal clocks that controlled various biological processes. But we did not know which processes related to growth interacted with the clock and how,” explains TiMet’s coordinator, Professor Andrew Millar from SynthSys at the University of Edinburgh, United Kingdom.

To unravel how the circadian rhythm contributes to plant growth, TiMet’s research team is focusing on two key metabolic pathways, which are a series of chemical reactions. The first of these pathways controls the organic compounds called isoprenoids, which include chlorophyll and plant hormones. The second governs the production of starch – the form in which plants store sugar – which is made during the day by photosynthesis.

Plants need a steady supply of sugar. Yet photosynthesis is impossible without light. Plants therefore gradually degrade their starch storage at night to avoid starving. “But the rate of degradation is carefully controlled. In fact, TiMet researchers found that plants effectively do an arithmetic division at the start of each night,” says Millar.

Tests on the small flowering plant, Arabidopsis thaliana, showed its circadian clock helps the plant predict the time until dawn. Arabidopsis thaliana then uses that information to determine the appropriate rate at which to break down its starch storage. This process is so precise that by dawn only 2 percent of the plant’s starch supply remains.

Unlike many other biological processes, this regulation of plant metabolism via the circadian clock cannot be triggered by external stimuli, TiMet research also showed. “At the beginning of our project there were early hints that the starch timer could be the internal clock – but no single lab had the capacity to understand it,” comments Millar. However, after combining different experimental measures on the small flowering plant, Arabidopsis thaliana, the TiMet team was able to show how starch regulation maintains the plant’s optimum growth rate in a 24-hour rhythm. Moved to a 20-hour cycle in a laboratory (with ten hours of light and ten of darkness per cycle), every artificial dawn surprises the plants and their growth rate significantly decreases.

Currently the TiMet team is using computers to model the growth of the whole plant. “The growth of the leaf rosette is particularly interesting to us,” adds Millar, “as this would provide a better grasp of how the parts used by humans, such as fruit, grow and thus benefit agriculture and forestry.” These industries are already using computer modelling to predict crop yield, however current models contain no direct genome (the genetic material of an organism) information. TiMet is the first project to link dynamic gene control to growth processes at the cell level. Millar explains that this is a big step “because although there are significant differences between our small Arabidopsis thaliana and a tree, our approach to link genetic and metabolic regulation to growth is transferable.” His expectation is that once the TiMet project is completed, its results could help prioritise particular varieties of crops, on the basis of their genomes, for field-testing.