Glutathione Promotes Susceptibility to <i>Meloidogyne incognita</i> 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 soilborne pathogens, particularly the economically important root-knot nematodes (<i>Meloidogyne</i> spp.), remains largely unexplored. Here, we investigated the role of glutathione in <i>Arabidopsis thaliana</i> during <i>M. incognita</i> 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 the roots of mutants in glutathione synthesis (<i>rax1</i>, <i>pad2</i>, <i>cad2</i>, and <i>nrc2</i>) significantly reduced gall formation by up to 27% and egg mass production by up to 33% compared with the control, suggesting its important role in nematode infection. Additionally, the exogenous application of glutathione increased plant susceptibility to <i>M. incognita</i>, resulting in a 23% increase in gall formation and a 19% increase in egg mass production compared with the mock-treated control. 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 <i>gstf6</i> loss-of-function lines, indicated that glutathione-dependent phytoalexin camalexin does not significantly contribute to <i>M. incognita</i> parasitism. These findings underscore the importance of glutathione in maintaining thiol homeostasis during the early stages of <i>M. incognita</i> infection and suggest that manipulating glutathione levels could be a potential strategy for nematode control in agriculture.