Glutathione as a Crucial Modulator of Phytohormone Signalling During Pathogen Defence in Plants

Plant's resistance to different stress factors is regulated by a complex signalling network which connects the individual signalling pathways, enabling them to fine tune their defence response. For more than last two decades, glutathione (GSH) is gradually gaining importance as a crucial player in this network. The present review summarizes the central role of GSH in modulating plant's defence response to biotic stress, specially emphasizing the molecular mechanism of these regulations. Several transgenic approaches to constitutively enhance GSH levels have been followed and in most cases, these transgenic plants exhibited enhanced biotic stress tolerance. The post 2000 era envisaged a mechanistic approach in this field and GSH has been shown to modulate the defence signalling network by cross-communication with several stress-related phytohormones. GSH imparts stress tolerance against biotrophic infection via NPR1-dependent salicylic acid (SA) mediated pathway. GSH regulates SA accumulation at the level of isochorismate synthetase 1 (ICS1) expression and can also act in NPR1-independent pathway. A synergistic GSH-ethylene (ET) interplay during necrotrophic infection has also been reported. It has been demonstrated that GSH induces ET biosynthesis by modulating transcriptional and post-transcriptional regulations of its key enzymes. The cross-talk of GSH with jasmonic acid (JA) and abscisic acid (ABA) in alleviating stress has been reported as well. However, mechanistic details of the interaction between GSH and JA or ABA signaling pathways are not elucidated in details.