Glutathione Promotes Susceptibility to Meloidogyne incognita by Modulating Thiol Homeostasis in Arabidopsis

Glutathione (l-γ-glutamyl-l-cysteinyl-glycine) is a key molecule that regulates numerous plant processes under both biotic and abiotic stress conditions. However, its role in plant responses to soil-borne pathogens, particularly the economically important root-knot nematodes (RKN; Meloidogyne spp.), remains largely unexplored. These nematodes are obligate biotrophs that establish specialized feeding sites—multinucleate giant cells—in host roots, manipulating plant biological processes. Here, we investigated the role of glutathione in Arabidopsis thaliana during RKN infection using a combination of genetic (glutathione biosynthetic mutants), biochemical (thiol and camalexin measurements), and pharmacological (exogenous glutathione supplementation) approaches. We found that glutathione depletion in roots of mutants in glutathione synthesis (rax1, pad2, cad2 and nrc2) significantly reduced gall formation and egg mass production, suggesting its important role in nematode infection. Additionally, the exogenous application of glutathione increased plant susceptibility to RKN. Biochemical analysis revealed that reduced glutathione levels disrupted the cysteine–glutathione balance early in the infection process. However, further assays, including camalexin measurements and infection assays with gstf6 loss-of-function lines, indicated that glutathione-dependent phytoalexins camalexin does not significantly contribute to RKN parasitism. These findings underscore the importance of glutathione in maintaining thiol homeostasis during the early stages of RKN infection and suggest that manipulating glutathione levels could be a potential strategy for nematode control in agriculture.