Glutathione and neodiosmin feedback sustain plant immunity.

Plants have evolved a two-layer immune system comprising pattern-triggered immunity (PTI) and effector-triggered immunity (ETI) that is activated in response to pathogen invasion. Microbial patterns and pathogen effectors can be recognized by surface-localized pattern-recognition receptors (PRRs) and intracellularly localized nucleotide-binding leucine-rich repeat receptors (NLRs) to trigger PTI and ETI responses, respectively. At present, the metabolites activated by PTI and ETI and their roles and signaling pathways in plant immunity are not well understood. In this study, metabolomic analysis showed that ETI and PTI induced various flavonoids and amino acids and their derivatives to accumulate in plants. Interestingly, the contents of glutathione and neodiosmin were specifically upregulated by ETI and PTI, respectively, which significantly enhanced plant immunity. Further studies showed that glutathione and neodiosmin failed to induce a plant immune response in which PRRs/coreceptors were mutated. In addition, glutathione-reduced mutant gsh1 analysis showed that GSH1 is also required for PTI and ETI. Finally, we propose a possible model in which glutathione and neodiosmin are considered signature metabolites induced in the process of ETI and PTI activation in plants and further continuous enhancement of plant immunity in which PRRs/coreceptors are needed. This model is beneficial for the in-depth understanding of the closed-loop mode of the positive feedback regulation of PTI and ETI signals at the metabolic level.