A bittersweet symphony: Metabolic signals in the circadian system

Unlocking Nature's Rhythms: Insights into Secondary Metabolite Modulation by the Circadian Clock

Plants, like many other living organisms, have an internal timekeeper, the circadian clock, which allows them to anticipate photoperiod rhythms and environmental stimuli to optimally adjust plant growth, development, and fitness. These fine-tuned processes depend on the interaction between environmental signals and the internal interactive metabolic network regulated by the circadian clock. Although primary metabolites have received significant attention, the impact of the circadian clock on secondary metabolites remains less explored. Transcriptome analyses revealed that many genes involved in secondary metabolite biosynthesis exhibit diurnal expression patterns, potentially enhancing stress tolerance. Understanding the interaction mechanisms between the circadian clock and secondary metabolites, including plant defense mechanisms against stress, may facilitate the development of stress-resilient crops and enhance targeted management practices that integrate circadian agricultural strategies, particularly in the face of climate change. In this review, we will delve into the molecular mechanisms underlying circadian rhythms of phenolic compounds, terpenoids, and N-containing compounds.

Identification of phospholipase Ds and phospholipid species involved in circadian clock alterations using CRISPR/Cas9-based multiplex editing of Arabidopsis

Reciprocal regulation between the circadian clock and lipid metabolism is emerging, but its mechanisms remain elusive. We reported that a lipid metabolite phosphatidic acid (PA) bound to the core clock transcription factors LATE ELONGATED HYPOCOTYL (LHY) and CIRCADIAN CLOCK ASSOCIATED1 (CCA1) and chemical suppression of phospholipase D (PLD)-catalyzed PA formation perturbed the clock in Arabidopsis. Here, we identified, among 12 members, specific PLDs critical to regulating clock function. We approached this using a multiplex CRISPR/Cas9 system to generate a library of plants bearing randomly mutated PLDs, then screening the mutants for altered rhythmic expression of CCA1 . All PLD s, except for β2 , were effectively edited, and the mutations were heritable. Screening of T2 plants identified some with an altered rhythm of CCA1 expression, and this trait was observed in many of their progenies. Genotyping revealed that at least two of six PLD s ( α1, α3 , γ1 , δ , ε and ζ2 ) were mutated in the clock-altered plants. Those plants also had reduced levels of PA molecular species that bound LHY and CCA1. This study identifies combinations of two or more PLDs and changes in particular phospholipid species involved in clock outputs and also suggests a functional redundancy of the six PLDs for regulating the plant circadian clock.

One sentence summary

This study identifies combinations of two or more phospholipase Ds involved in altering clock outputs and the specific phosphatidic acid species impacting the clock rhythms.

Time for growth

Plants measure the duration of metabolic activity to promote rapid growth in long days.

Transcriptional and post-translational regulation of plant autophagy

In response to changing environmental conditions, plants activate cellular responses to enable them to adapt. One such response is autophagy, in which cellular components, for example proteins and organelles, are delivered to the vacuole for degradation. Autophagy is activated by a wide range of conditions, and the regulatory pathways controlling this activation are now being elucidated. However, key aspects of how these factors may function together to properly modulate autophagy in response to specific internal or external signals are yet to be discovered. In this review we discuss mechanisms for regulation of autophagy in response to environmental stress and disruptions in cell homeostasis. These pathways include post-translational modification of proteins required for autophagy activation and progression, control of protein stability of the autophagy machinery, and transcriptional regulation, resulting in changes in transcription of genes involved in autophagy. In particular, we highlight potential connections between the roles of key regulators and explore gaps in research, the filling of which can further our understanding of the autophagy regulatory network in plants.

The strigolactone pathway plays a crucial role in integrating metabolic and nutritional signals in plants

Strigolactones are rhizosphere signals and phytohormones that play crucial roles in plant development. They are also well known for their role in integrating nitrate and phosphate signals to regulate shoot and root development. More recently, sugars and citrate (an intermediate of the tricarboxylic acid cycle) were reported to inhibit the strigolactone response, with dramatic effects on shoot architecture. This Review summarizes the discoveries recently made concerning the mechanisms through which the strigolactone pathway integrates sugar, metabolite and nutrient signals. We highlight here that strigolactones and MAX2-dependent signalling play crucial roles in mediating the impacts of nutritional and metabolic cues on plant development and metabolism. We also discuss and speculate concerning the role of these interactions in plant evolution and adaptation to their environment.

The Regulatory Networks of the Circadian Clock Involved in Plant Adaptation and Crop Yield

Global climatic change increasingly threatens plant adaptation and crop yields. By synchronizing internal biological processes, including photosynthesis, metabolism, and responses to biotic and abiotic stress, with external environmental cures, such as light and temperature, the circadian clock benefits plant adaptation and crop yield. In this review, we focus on the multiple levels of interaction between the plant circadian clock and environmental factors, and we summarize recent progresses on how the circadian clock affects yield. In addition, we propose potential strategies for better utilizing the current knowledge of circadian biology in crop production in the future.