BIG Regulates the Circadian Clock and Development

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Due to population growth and changing environments there is an urgent need to understand the basic biology that regulates the yield of crop plants. We have recently discovered that a protein called BIG is involved in the regulation of plant development and the ability of plants to tell the time. We will resolve how BIG exerts such profound effects on the growth of plants. We will do this by investigating the regulation of circadian clocks in plants, and the relationship between the role of BIG in the circadian clock with pathways by which hormones regulate plant development. Breeders of wheat, barley, tomato and many other crops have through traditional breeding altered the genes involved in the circadian clock to increase productivity. We are interested in identifying the cellular mechanisms by which plants ensure that cellular processes occur at the correct time of day. For example, just before dawn plants prepare the photosynthetic machinery to be ready for the rising of the sun, whereas at night, process involved in the breakdown of storage sugars to provide energy for surviving the dark of the night come to the fore. The correct timing of biological events is regulated by internal circadian clocks, similar in concept to those that regulate human sleep and wake cycles. In plants, circadian clocks control many activities including the opening and closing of flowers, changes in gene activity and the timing of starch production and degradation. The circadian clock, present in every cell, is made of circuits of genes that are active at specific times of the day or night. These genes regulate each other to form an oscillator that can be conceptualised as a molecular watch. The circadian clock is popularly considered a 24 h clock, but this is not strictly correct, the period of the circadian clock of Arabidopsis, and other organisms is variable. We have discovered that cellular sugars speed up the circadian clock and a common metabolite, nicotinamide, makes the clock run more slowly. Our studies have identified a protein that is required for the correct control of circadian speed, this protein is called BIG. We will discover which circadian clock genes change behaviour in response to altered function of BIG and identify proteins that interact with BIG to regulate the speed of the circadian oscillator. We will discover if BIG is involved in the response to nicotinamide alone, or also participates in changes in circadian speed caused by sugars, light signals and hormones. We will discover if BIG affects the ability of plant circadian clocks to respond to the changing time of dawn by examining the timing of gene expression and leaf movements in light and dark cycles of different lengths. We will use this information to investigate how BIG also contributes to hormonal signalling and the regulation of development. We will determine if BIG affects both the circadian clock and hormonal control of plant development because these two processes are closely related, or because BIG has separate functions in different processes. These studies will begin to resolve how BIG, a major regulator of many aspects of the functioning of a plant, exerts its effects. This work will be performed in a simple plant suited to laboratory studies, with the ultimate goal of understanding how important biological responses in crop plants control the major traits of the crops.