Auxin clock: circadian auxin homeostasis

The circadian clock acclimates organisms to daily changing environmental conditions by regulating signalling, metabolic and hormonal response pathways. Plants with a well-functioning clock acclimate more successfully to a broad range of stress conditions. The plant hormone auxin is a key regulator of almost all aspects of plant growth and development, including adaptive responses. A large proportion of auxin genes are regulated by the circadian clock. We recently showed that auxin levels themselves display circadian oscillations in Arabidopsis thaliana (referred to as auxin clock; VoB et al., 2015 Nature Comms 6, 7641). Climate predictions indicate that crops will have to be grown at more extreme climate conditions and at different latitudes, which come with a change in day length. Glasshouse grown vegetables could also be grown in different, more optimal day lengths or temperatures if that would improve yield or shorten their generation time. Therefore it is crucial to understand how the crosstalk of circadian clock and auxin signalling pathways contributes to developmental decisions at the whole plant level. The BBSRC DTP project will fill this knowledge gap by answering the following questions: 1. How does the auxin clock contribute to plant growth and fitness? 2. To what extent does auxin homeostasis contribute to the auxin clock? 3. How tissue and context specific is the auxin clock, and how is this regulated? This will be achieved this by generating transgenic Arabidopsis lines in which auxin homeostasis and/or signalling is uncoupled from the circadian clock. Candidate genes have been selected from published circadian transriptomic and RNAseq datasets. Lines displaying disturbed auxin oscillations will be compared to wildtype at different daylengths for growth dynamics, flowering time, photosynthetic activity and root/shoot branching. Heat, cold, drought and nutrient stress will be tested, as they have been linked to the circadian clock and auxin signalling. Lines displaying strong phenotypes will be further analysed using RT-qPCR, RNAseq, MS based metabolic profiling (in collaboration with Karin Ljung, Umeå University, Sweden). We will use equipment in Nottingham to time-lapse image circadian fluxes in shoot and root using Confocal- and Lightsheet Microscopes and a Luciferase Camera. Comparing a collection of Arabidopsis thaliana ecotypes for classic circadian growth patterns, such as leaf movement and oscillating shoot elongation will give insight into under which conditions the auxin clock is of higher importance for fitness.