BIG Regulates the Circadian Clock and Development

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.

Webb and Leyser have decided to combine forces to understand how BIG, a calossin-like protein of unknown function, has profound effects on plant light and hormone signalling, circadian rhythms and growth. Webb and Leyser have been prompted to investigate BIG because they have independently discovered that BIG regulates the synchronisation between the external circadian clock and external rhythms of light and dark, and strigolactone signalling. The effect of BIG mutations are profound and widespread. It is clear that an understanding of plant signalling, will require knowledge of how BIG exerts its effects. We will build on our discoveries to identify how BIG regulates circadian entrainment and plant development. We will determine how BIG regulates circadian period by identifying the transcriptional responses in the oscillator affected by mutation. We will perform entrainment studies such as measuring phase changes in response to a range of stimuli and growth in non-24 h light/dark cycles to determine the roles of BIG in establishing correct circadian phase and entrainment. We will identify how BIG exerts its effect on circadian rhythms and strigolactone signalling by identifying BIG protein binding partners, and investigating the role of these binding proteins in the circadian and strigolactone signalling pathways. To determine if the wide-ranging effects of BIG are due to integrative or multifunctional effects we will investigate the relationship between the circadian clock and strigolactone. Potential targets for crop improvement will be shared with industrial partners.

IMPACT STATEMENT
Understanding plant growth and biomass accumulation is crucial to maintaining improvements in crop productivity, particularly as climate changes. BIG is a key regulator of growth. We will determine how BIG regulates growth, development and ensures that biological events occur at the correct time of day. Our work will be performed in the model plant Arabidopsis because the goals of the research can only be achieved with access to the genetic resources of this organism. Our approach considers a network that might apply also to the major crops. The data from this study will be fed in to other studies in the Webb lab that are considering the role of the circadian oscillator in wheat. Our project therefore has potential impact for the agrifood/plant breeding sector, as well as providing great opportunities for public engagement.

AGRIFOOD IMPACT
We anticipate that there will be many agricultural stakeholders interested in the work. Circadian rhythms regulate the interactions of the plant with both the abiotic and biotic environment. As climate changes, the security of many food crops is likely to be compromised, and strategies to maintain food supply will require objective scientific evidence about the relationships between plants and their environment, along with an understanding of how genetic pathways control development of relevant plant traits. Commercial ventures interested in maximising agricultural output are obvious partners
in maximising impact of this work as are crop breeders.
We will disseminate data to farmers and breeders, and increase our engagement with stakeholders, through activities at the University and at the National Institute for Agricultural Botany (NIAB). We will target outreach to these stakeholders through AARW's current contacts with Bayer Crop Science and a number of plant breeders, and through the University's "Enterprise Tuesdays", where research can be presented informally to interested industrial and agricultural partners.
Results will be demonstrated at NIAB Innovation Farm Open Days and Symposia.
IMPACT THROUGH PUBLIC ENGAGEMENT
Other users who will be interested in this work include the general public, who we know, through previous engagement activities, are fascinated to learn about the intricacies of plant biology. The recent Novel Prize for Medicine recognising members of the circadian research community has raised the public profile of the study of circadian rhythms in plants. Public engagement about natural systems is nationally and internationally becoming increasingly important, as public concerns, fuelled by constant media coverage, are an important factor in promoting dialogue at all governmental policy levels concerning our treatment and management of environmental and agricultural systems.
We will present our project at public engagement events such as in-house University events tied with National Science Week (annually in March), Cambridge Festival of Plants (annually in May) and the Cambridge Festival of Ideas (annually in October). In addition, we will work with the Horticulture, Education and Interpretation staff at Cambridge University Botanic Garden to a trail through the Garden, leading visitors to a variety of plants with particular developmental, metabolic or life cycle traits associated with circadian rhythms. The Cambridge University Botanic Garden hosts 250,000 casual visitors per year, plus 12,000 schoolchildren on arranged visits, so this display will reach a large and varied audience.
Research findings will be made freely available on this site after their assessment by Cambridge Enterprise for potential IP issues.