Unraveling the molecular interconnections between circadian rhythms and lipid metabolism

PROJECT SUMMARY Circadian clocks drive the 24-hour rhythms regulating many aspects of metabolism whereas metabolic activities modulate the clock function. Dysfunction of the clock is associated with metabolic disorders, compromising organismal response to the environment. However, the molecular interplay between metabolism and the clock and, in particular, the mechanism by which metabolism affects clock functions are not well understood. Recent studies indicate that phosphatidic acid (PA), a central lipid metabolic intermediate and important lipid messenger, interacts with the core clock transcription factors LATE ELONGATED HYPOCOTYL (LHY) and CIRCADIAN CLOCK ASSOCIATED 1 (CCA1), and genetic and chemical manipulations of PA levels alter the clock functions in Arabidopsis. PA and its production enzymes, phospholipase D (PLD) and diacylglycerol (DAG) kinase (DGK), affect various cellular and pathophysiological processes in humans and other organisms. These findings suggest that specific lipid-clock factor interactions may act as a molecular conduit to integrate metabolic and clock activities. They further indicate that PA signaling acts in nuclei, affecting critical nuclear processes, but its cellular actions have been studied primarily outside the nucleus. Thus, this research aims to fill three key knowledge gaps: 1) how PA mediates nuclear processes; 2) how PA and lipid metabolism modulate the clock; and 3) how the molecular clock regulates lipid metabolism, by addressing several interlaced questions and challenges: What are the subnuclear locations of PA-protein interactions, the effect of PA on stress-induced DNA repair and transcription, the lipid-clock interactome, and the impact of clock perturbations on specific lipid metabolic processes? Additionally, how do lipid-clock interplays affect stress responses? Could the lipid-clock interplay be modulated to improve organismal resilience to adverse environments and lipid production? These questions will be approached by integrating multiple open-ended and targeted strategies, including lipid imaging in vivo, subcellular lipidomics, lipid-protein interactome, multiplex genomic editing, non-invasive phenotyping, and deploying extensive genetic and analytical resources developed in the model organism Arabidopsis. The mechanistic study of PA’s action in nuclei will advance the understanding of the emerging lipid mediator PA, such as its role in mitogenesis and stress responses. Unraveling the molecular interplays between the clock and lipids will elucidate the mechanism by which lipid metabolic malfunctions perturb the clock function and, conversely, clock disruptions lead to metabolic dysfunctions. In addition, the study will advance the functional understanding of PLD and DGK and have potential applications to improve plant resilience to environmental stress and lipid production. Because the basic molecular mechanism of the clock is conserved between plants and humans, and the molecular clock, PA, and its production enzymes play important roles in pathophysiological process, the findings from this research have significant relevance to public health.