Role of TCP transcription factors on the regulation of the circadian clock function in plants

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Agriculture intensification and expansion of production areas are expected to provide higher crop yields needed to accommodate future demands of food and energy. To achieve optimal growth performance, plants strongly rely on their ability to properly interact with their environment. In fact, most plant responses exhibit circadian rhythms (oscillations repeated every 24 hours) that are in synchrony with daily rhythms in environmental cues, such as light and temperature. A timekeeping mechanism, known as the circadian clock, is critical to maintain the pace of circadian responses according to oscillations in external cues. Notably, fine-tuning the clock pace was suggested to allow adaptation of crop species to grow at different latitudes. The plant clock function is regulated by multiple environmental cues, which in nature are present simultaneously. However, in most studies the role of different cues was investigated in isolation. Thus, how combined signals modulate the plant clock remains a largely unexplored area that could provide critical insights to understanding how plant responses are regulated in a natural setting. This project aims at filling this gap-in-knowledge by exploring novel mechanisms of clock regulation in plants grown under combined light and temperature cycles. In particular, the role of previously unrecognized clock components that differentially respond to these environmental cues will be investigated. Furthermore, this project will implement a systematic training program that will offer exceptional student research opportunities. Finally, given the conserved clock architecture among plant species, results from this project could also illuminate novel approaches to improve crops in future agricultural settings. At the molecular level, the clock function relies on a heavily integrated transcriptional network. The transcription factors (TFs) CCA1 and LHY are core components of this network and the timing of CCA1 and LHY expression is critical to set the clock pace. Despite their important role, the mechanisms that regulate CCA1 and LHY expression by environmental signals other than light cycles have remained elusive. By developing a pioneering strategy, the principal investigator identified a TF from the TCP family, called CHE, that regulates the CCA1 promoter activity and plays an important role for the clock function. Preliminary results indicate that other TCPs interact with the CCA1 promoter and CHE protein, as well as the LHY promoter. Furthermore, some of the identified TCPs exhibit a differential expression pattern when plants are grown in combined light and temperature cycles. Thus, the overall hypothesis of this project is that the plant clock function relies on the coordinated role of TCP TFs to regulate CCA1 and LHY expression. The proposed studies are expected to reveal novel mechanistic insights of the clock regulation in plants and, by including combined light and temperature cycles, to provide an unprecedented assessment of how the plant clock functions in nature. Finally, this research will provide proof of principle for the power of improved TF screening approaches that could be used to understand transcriptional mechanisms not only in plants but also other species.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.