Low glutathione regulates gene expression and the redox potentials of the nucleus and cytosol in Arabidopsis thaliana

Reduced glutathione (GSH) is considered to exert a strong influence on cellular redox homeostasis and to regulate gene expression, but these processes remain poorly characterized. Severe GSH depletion specifically inhibited root meristem development, while low root GSH levels decreased lateral root densities. The redox potential of the nucleus and cytosol of Arabidopsis thaliana roots determined using roGFP probes was between -300 and -320mV. Growth in the presence of the GSH-synthesis inhibitor buthionine sulfoximine (BSO) increased the nuclear and cytosolic redox potentials to approximately -260mV. GSH-responsive genes including transcription factors (SPATULA, MYB15, MYB75), proteins involved in cell division, redox regulation (glutaredoxinS17, thioredoxins, ACHT5 and TH8) and auxin signalling (HECATE), were identified in the GSH-deficient root meristemless 1-1 (rml1-1) mutant, and in other GSH-synthesis mutants (rax1-1, cad2-1, pad2-1) as well as in the wild type following the addition of BSO. Inhibition of auxin transport had no effect on organ GSH levels, but exogenous auxin decreased the root GSH pool. We conclude that GSH depletion significantly increases the redox potentials of the nucleus and cytosol, and causes arrest of the cell cycle in roots but not shoots, with accompanying transcript changes linked to altered hormone responses, but not oxidative stress. Reduced glutathione (GSH) is a multifunctional metabolite with important (but poorly defined roles) in the regulation of cellular redox homeostasis and gene expression. GSH deficiency in the Arabidopsis thaliana root meristemless 1-1 (rml1-1) mutant or in the wild type seedlings treated with the GSH synthesis inhibitor buthionine sulfoximine (BSO) led to an increase of over 40mV in the redox potentials of the nuclei and cytosol of the root cells. Low GSH levels had a major impact on gene expression. The GSH-responsive genes that were identified include transcription factors and proteins involved in the cell cycle, redox regulation and hormone signalling. Low GSH availability in other GSH synthesis mutants (such as rax1-1, cad2-1 and pad2-1) decreased lateral root densities. The addition of auxin decreased the root glutathione pool. We conclude that GSH deficiency exerts a strong influence over auxin signalling in the absence of effects on oxidative signalling pathways.