Considering that circadian clocks were first discovered in plants, and studied almost exclusively in plants for almost a century before people started looking at animals in the early 20th century, it is somewhat surprising that the molecular aspects of the circadian rhythm generation mechanisms have lagged behind those in insects, vertebrates, fungi and bacteria. It is always nice to see a paper reporting a discovery of a new plant clock gene:
Plants set their clocks by detecting the light cycle, and Chua’s lab found that an accessory protein, called SPA1, is important for keeping the internal clock set. When they bred Arabidopsis plants with a mutated SPA1 protein, the plants flowered early, producing shoots and flowers weeks ahead of wild-type plants.
“The regulation of flowering initiation in response to the length of the day is mediated by the interaction of light with the plant s circadian clock system,” says Chua. Plants detect light with proteins called phytochromes and cryptochromes. SPA1 regulates one of these phytochromes, called PhyA.
The PhyA protein links light detection with the circadian clock system and directly influences when a plant flowers. But Chua’s finding suggests that SPA1 normally represses PhyA function, holding the plant back from flowering until the right time. “We knew that SPA1 negatively regulated PhyA immediately after germination, but didn t know if it played a role in the adult,” says Chua. “Our results show that SPA1 is important in the adult for regulating PhyA and the circadian period. When SPA1 is mutated, the plants precociously flower, affecting their entire reproductive cycle.”