JAC1 Promotes Thermotolerance in Arabidopsis by Limiting Heat-Induced H2O2 Accumulation and Protecting PGLP1 from Sulfenylation-Mediated Inhibition

Heat stress is a major constraint on plant growth and productivity, and excessive accumulation of reactive oxygen species (ROS) and reactive nitrogen species (RNS), especially hydrogen peroxide (H₂O₂), is a primary cause of heat-induced cellular damage. Photorespiration becomes accelerated at high temperature and generates the toxic metabolite 2-phosphoglycolate (2PG), whose accumulation is prevented by the first photorespiratory enzyme 2-phosphoglycolate phosphatase (PGLP1). Here, we identify the auxilin-like J-domain protein JAC1 (AT1G75100) as a positive regulator of thermotolerance in <i>Arabidopsis thaliana</i> (<i>A. thaliana</i>). <i>JAC1</i> transcripts were rapidly induced by heat treatment, and loss-of-function <i>jac1</i> mutants (<i>jac1-1</i> and <i>jac1-2</i>) were hypersensitive to long-term heat stress (38 °C, 7 d), whereas three independent <i>JAC1</i> overexpression lines (#2, #4, #5) exhibited enhanced survival. Consistent with a role in ROS homeostasis, heat-treated <i>jac1</i> mutants showed stronger DAB staining, consistent with higher apparent H₂O₂ levels, whereas <i>JAC1</i> overexpression lines showed weaker staining. Although PGLP1 abundance (mRNA and protein) was unchanged among genotypes, heat treatment (38 °C, 12 h) caused a marked reduction in leaf PGLP1 enzymatic activity in <i>jac1</i> mutants and a significant increase in <i>JAC1</i> overexpression lines, leading to corresponding changes in 2PG content. PGLP1 sulfenylation, a H₂O₂-dependent post-translational modification that inhibits PGLP1, was detectable only after heat and was enhanced in <i>jac1</i> mutants but suppressed in <i>JAC1</i> overexpression lines. Genetic manipulation of <i>PGLP1</i> supported that <i>PGLP1</i> functions downstream of <i>JAC1</i>: overexpressing <i>PGLP1</i> in <i>jac1-1</i> rescued heat sensitivity, whereas knocking down <i>PGLP1</i> in the <i>JAC1</i> overexpression background reversed thermotolerance. Together, our results support a model in which JAC1 maintains heat-induced H₂O₂ homeostasis, thereby limiting PGLP1 sulfenylation, sustaining PGLP1 activity and preventing toxic 2PG accumulation during heat stress.