Regulation of Nitrate (NO) Transporters and Glutamate Synthase-Encoding Genes under Drought Stress in Arabidopsis: The Regulatory Role of Transcription Factor.

Nitrogen (N) is an essential macronutrient, which contributes substantially to the growth and development of plants. In the soil, nitrate (NO) is the predominant form of N available to the plant and its acquisition by the plant involves several NO transporters; however, the mechanism underlying their involvement in the adaptive response under abiotic stress is poorly understood. Initially, we performed an in silico analysis to identify potential binding sites for the basic leucine zipper 62 transcription factor ( TF) in the promoter of the target genes, and constructed their protein-protein interaction networks. Rather than , results revealed the presence of -regulatory elements specific to two other bZIP TFs, and . A recent report showed that TF negatively regulated and . Therefore, we investigated the transcriptional regulation of (low-affinity NO transporter), (dual-affinity NO transporter), and (high-affinity NO transporters), and and (both encoding glutamate synthase) in response to drought stress in Col-0. From the perspective of exploring the transcriptional interplay of the target genes with TF, we measured their expression by qPCR in the (lacking the gene) under the same conditions. Our recent study revealed that TF positively regulates the expression of (, a key gene of the de novo pyrimidine biosynthesis pathway know to share a common substrate with the N metabolic pathway). For this reason, we included the mutant in the study. Our findings revealed that the expression of , and was similarly regulated in and but differentially regulated between the mutant lines and Col-0. Meanwhile, the expression pattern of in was similar to that observed in Col-0 but was suppressed in . The breakthrough is that had the highest expression level in Col-0, while being suppressed in and . Furthermore, the transcript accumulation of and showed differential regulation patterns between Col-0 and , and . Therefore, results suggest that of all tested NO transporters, is thought to play a preponderant role in contributing to NO transport events under the regulatory influence of TF in response to drought stress.