Heat-induced methylglyoxal impairs plant thermotolerance by repressing cpHSC70-1-mediated chloroplast protein import via post-translational modification.
Global warming threatens agricultural productivity, making it crucial to understand how plants perceive and respond to heat stress. Although various metabolic pathways are known to participate in plant heat responses, the role of metabolites in post-translational regulation under heat stress remains poorly understood. Here, we report that methylglyoxal (MG) functions as a negative modulator of plant thermotolerance. We demonstrate that heat stress induces the accumulation of the photorespiratory metabolite 2-phosphoglycolate (2PG), which inhibits the activity of plastid triose phosphate isomerase (pdTPI), leading to increased MG levels. Through a proteomic approach, we identified the chloroplast chaperone cpHSC70-1 as a primary target of MG. MG modifies cpHSC70-1 at a conserved arginine residue (R373), inhibiting its ATPase activity and consequently impairing chloroplast protein import under heat stress. Genetic evidence confirms that the 2PG-pdTPI module controls MG accumulation, and that MG exerts its thermosensitive effect through cpHSC70-1. Our work reveals a photorespiratory metabolite-driven post-translational regulatory pathway, elucidating a novel mechanism for metabolic control of plant thermotolerance.