Glutathione regulates transcriptional activation of iron transporters via S-nitrosylation of bHLH factors to modulate subcellular iron homeostasis

Abstract

While glutathione (GSH) is known to regulate iron (Fe) deficiency response in plants, its involvement in modulating subcellular Fe homeostasis remained elusive. In this study, we report that the GSH depleted mutants, cad2-1 and pad2-1 displayed increased sensitivity to Fe deficiency with significant down-regulation of the vacuolar Fe exporters, AtNRAMP3 and AtNRAMP4 and the chloroplast Fe importer, AtPIC1. Moreover, the pad2-1 mutant accumulated higher Fe content in vacuoles and lower in chloroplasts compared with Col-0 under Fe limited condition. Exogenous GSH treatment could enhance the chloroplast Fe content in Col-0 plants but failed to do so in the nramp3nramp4 double mutant demonstrating the role of GSH in modulating subcellular Fe homeostasis. Pharmacological experiments, mutant analysis and promoter assay revealed that this regulation involved transcriptional activation of the transporter genes by a GSH-GSNO module. The Fe responsive bHLH transcription factors (TFs), AtbHLH29, AtbHLH38 and AtbHLH101 were identified to interact with the promoters of these genes which were in turn activated via S-nitrosylation. Together, the present study delineates the role of GSH-GSNO module in regulating subcellular Fe homeostasis by transcriptional activation of the Fe transporters AtNRAMP3, AtNRAMP4 and AtPIC1 via S-nitrosylation of the bHLH TFs during Fe deficiency. Summary statementGlutathione regulates subcellular iron homeostasis under iron deficiency via GSNO dependent transcriptional activation of AtNRAMP3, AtNRAMP4 and AtPIC1 genes by S-nitrosylation of the iron responsive bHLH transcription factors, AtbHLH29, AtbHLH38 and AtbHLH101.