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 Arabidopsis thaliana (A. thaliana). JAC1 transcripts were rapidly induced by heat treatment, and loss-of-function jac1 mutants (jac1-1 and jac1-2) were hypersensitive to long-term heat stress (38 °C, 7 d), whereas three independent JAC1 overexpression lines (#2, #4, #5) exhibited enhanced survival. Consistent with a role in ROS homeostasis, heat-treated jac1 mutants showed stronger DAB staining, consistent with higher apparent H2O2 levels, whereas JAC1 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 jac1 mutants and a significant increase in JAC1 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 jac1 mutants but suppressed in JAC1 overexpression lines. Genetic manipulation of PGLP1 supported that PGLP1 functions downstream of JAC1: overexpressing PGLP1 in jac1-1 rescued heat sensitivity, whereas knocking down PGLP1 in the JAC1 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.