The primary nitrate response TGA1 and TGA4 transcription factors are negative regulators of sulfate uptake and metabolism
Abstract Although the synergistic effects of nitrogen (N) and sulfur (S) on crop performance are well established, the regulatory network integrating these pathways remains largely unknown. Clade I TGA transcription factors (TFs), TGA1 and TGA4, function within the second and third layers of the primary nitrate-responsive transcriptional cascade and are also implicated in immunity. Here we show that provision of nitrate rapidly induces sulfate uptake and assimilation through a yet undefined mechanism, followed by a delayed repression of SULTR1;2 mediated by clade I TGA transcription factors. In contrast, clade II TGAs and the nitrate signaling components NRT1.1 and NLP7 were not involved in this regulation. The binding analysis showed that both TGA1 and TGA4 bind to the promoter of the high-affinity sulfate transporter SULTR1;2, while in vivo assay confirmed that TGA1 and TGA4 repress the activity of AtSULTR1;1 and AtSULTR1;2 promoters. Genetic and biochemical analysis further revealed that clade I TGA TFs negatively regulate sulfur metabolism not only under nitrate provision, but also under sulfate starvation. Accordingly, the tga1 tga4 double mutant displayed enhanced sulfate uptake, increased cysteine accumulation, and improved fitness under long-term sulfate limitation. Additionally, TGA1 and TGA4 influenced sulfur-containing secondary metabolism, including indolic glucosinolates and camalexin during biotic stress. By coordinating sulfate acquisition with nitrogen signaling, clade I TGAs contribute to maintaining nutrient homeostasis and plant performance. This work advances our understanding of mineral nutrient integration in plants and provides new perspectives for improving nutrient use efficiency and stress resilience in crops.