Glutathione activates PHT1;5 gene via WRKY75 transcription factor to regulate phosphate homeostasis in Arabidopsis

Phosphorus is a macronutrient that regulates a wide range of physiological processes, including plant growth and development. The scarcity of bioavailable inorganic phosphate (Pi) is often a constraint for plant growth in most agricultural ecosystems. Under Pi-limited conditions, plants increase Pi acquisition or alter Pi distribution within tissues by activating different Pi transporters and Pi starvation-induced genes. Glutathione (GSH), on the other hand, is known to play a critical role in regulating iron and zinc homeostasis in Arabidopsis. However, how it regulates Pi homeostasis under Pi-limited conditions remains unexplored. We found that the two GSH-deficient mutants, cad2-1, and pad2-1, were hypersensitive to Pi starvation. Under Pi-sufficient condition, the root Pi content was lower in the mutants but significantly higher in the shoot over the Col-0 plants. The pattern was reversed under Pi-deficient condition. Interestingly, among the different Pi transporters analyzed, the AtPHT1;5 was significantly down-regulated in the two GSH-deficient mutants. Treatment with exogenous GSH could alter Pi accumulation in Col-0 and the pht1;5 complementation lines but not in the pht1;5 mutant. This observation confirmed the role of GSH in Pi reallocation during Pi starvation via the AtPHT1;5 transporter. Further, promoter analysis demonstrated that GSH regulates the transcription of the AtPHT1;5 gene. The Pi-responsive transcription factor (TF), AtWRKY75 was identified to interact with the AtPHT1;5 promoter, and Pi deficiency or GSH treatment enhanced its binding affinity. Together our investigation delineates that GSH regulates the AtPHT1;5 transporter via the AtWRKY75 TF to modulate Pi distribution under altered Pi conditions. Summary statement Glutathione regulates Pi translocation in Arabidopsis under Pi deficiency via transcriptional activation of AtPHT1;5 gene by the Pi-deficiency responsive AtWRKY75 transcription factor.