Tomato GLR3.3 and GLR3.5 mediate cold acclimation-induced chilling tolerance by regulating apoplastic H2O2 production and redox homeostasis

Plant glutamate receptor-like (GLR) genes play important roles in plant development and immune response. However, the functions of GLRs in abiotic stress response remain unclear. Here we show that cold acclimation at 12 degrees C induced the transcripts of GLR3.3 and GLR3.5 with increased tolerance against a subsequent chilling at 4 degrees C. Silencing of GLR3.3 or/and GLR3.5 or application of the antagonist of ionotropic glutamate receptor 6,7-dinitroquinoxaline-2,3-dione (DNQX), all compromised the acclimation-induced increases in the transcripts of respiratory burst oxidase homolog1 (RBOH1), activity of NADPH oxidase, the accumulation of apoplastic H2O2 and the ratio of reduced glutathione (GSH) to oxidized glutathione (GSSG), resulting in an attenuated chilling tolerance; the effect, however, was rescued by foliar application of H2O2 or GSH. Both RBOH1-silenced and glutathione biosynthesis genes, gamma- glutamylcysteine synthetase (GSH1)- and glutathione synthetase (GSH2)-cosilenced plants had decreased chilling tolerance with reduced GSH/GSSG ratio. Moreover, application of DNQX had little effects on the GSH/GSSG ratio and the tolerance in RBOH1-silenced plants and GSH1- and GSH2-cosilenced plants. These findings unmasked the functional hierarchy of GLR-H2O2-glutathione cascade and shed new light on cold response pathway in tomato plants.