SnRK1 and TOR: central regulators of autophagy in plant energy stress responses

Abstract

Plants harness light through photosynthesis to produce chemical energy, a cornerstone of life on Earth. However, environmental challenges, such as insufficient light, nutrient deficiencies, and abiotic stresses, often disrupt energy availability, compelling plants to activate autophagy. This process degrades superfluous or damaged cellular components to recycle building blocks for vital functions. Like animals and yeast, plants employ conserved energy-sensing pathways, notably the antagonistic SNF1-related kinase 1 (SnRK1; homologous to AMP-activated protein kinase in animals) and target of rapamycin (TOR) signaling cascades. Plants have also evolved unique strategies to initiate autophagy when faced with energy stress. Recent studies have elucidated plant-specific mechanisms, including the pivotal role of FCS-like zinc finger proteins in integrating stress and metabolic signals to modulate SnRK1 and TOR activity. This review synthesizes the current understanding of autophagy regulation in plants under energy stress, emphasizing how SnRK1 and TOR orchestrate cellular homeostasis. It also examines organelle-phagy—chlorophagy, mitophagy, and lipophagy—in sustaining energy balance during stress. Amid intensifying climate challenges, including drought, nutrient scarcity, and erratic weather, elucidating these mechanisms is critical for engineering crops with enhanced resilience and productivity, thereby addressing global food security challenges. Furthermore, as autophagy is conserved across eukaryotes, plant research offers insight into universal cellular processes, potentially informing applications related to human health. This review also consolidates recent advances and proposes future research to deepen our understanding of energy signaling and autophagy in plants.