Carbon/nitrogen metabolism and stress response networks - calcium-dependent protein kinases as the missing link?

Calcium-dependent protein kinases (CDPKs) play essential roles in plant development and stress responses. CDPKs have a conserved kinase domain, followed by an auto-inhibitory junction connected to the calmodulin-like domain that binds Ca2+. These structural features allow CDPKs to decode the dynamic changes in cytoplasmic Ca2+ concentrations triggered by hormones and by biotic and abiotic stresses. In response to these signals, CDPKs phosphorylate downstream protein targets to regulate growth and stress responses according to the environmental and developmental circumstances. The latest advances in our understanding of the metabolic, transcriptional, and protein-protein interaction networks involving CDPKs suggest that they have a direct influence on plant carbon/nitrogen (C/N) balance. In this review, we discuss how CDPKs could be key signaling nodes connecting stress responses with metabolic homeostasis, and acting together with the sugar and nutrient signaling hubs SnRK1, HXK1, and TOR to improve plant fitness.

Turning the Knobs: The Impact of Post-translational Modifications on Carbon Metabolism.

Plants rely on the carbon fixed by photosynthesis into sugars to grow and reproduce. However, plants often face non-ideal conditions caused by biotic and abiotic stresses. These constraints impose challenges to managing sugars, the most valuable plant asset. Hence, the precise management of sugars is crucial to avoid starvation under adverse conditions and sustain growth. This review explores the role of post-translational modifications (PTMs) in the modulation of carbon metabolism. PTMs consist of chemical modifications of proteins that change protein properties, including protein-protein interaction preferences, enzymatic activity, stability, and subcellular localization. We provide a holistic view of how PTMs tune resource distribution among different physiological processes to optimize plant fitness.