Glutathione regulates subcellular iron homeostasis via transcriptional activation of iron responsive genes in Arabidopsis

Abstract

Glutathione (GSH) is a ubiquitous molecule known to regulate various physiological and developmental phenomena in plants. Recently, its involvement in regulating iron (Fe) deficiency response was established in Arabidopsis. However, the role of GSH in modulating subcellular Fe homeostasis remained elusive. In this study, we dissected the role of GSH in regulating Fe homeostasis in Arabidopsis shoots under Fe limited conditions. The two GSH depleted mutants, cad2-1 and pad2-1 displayed increased sensitivity to Fe deficiency with smaller rosette diameter and higher chlorosis level compared with the Col-0 plants. Interestingly, the expression of the vacuolar Fe exporters, AtNRAMP3 and AtNRAMP4, chloroplast Fe importer, AtPIC1, along with AtFer1 and AtIRT1 were significantly down-regulated in these mutants. The expression of these genes were up-regulated in response to exogenous GSH treatment while treatment with BSO, a GSH inhibitor, down-regulated their expression. Moreover, the mutants accumulated higher Fe content in the vacuole and lower in the chloroplast compared with Col-0 under Fe limited condition suggesting a role of GSH in modulating subcellular Fe homeostasis. This regulation was, further, found to involve a GSNO-dependent pathway. Promoter analysis revealed that GSH induced the transcription of these genes presumably via S-nitrosylation of different Fe responsive bHLH transcription factors.