Plants activate glutathione (GSH)-dependent detoxification pathways at biochemical and molecular levels under boron (B) toxicity. Sulfate uptake and transport are necessary for GSH biosynthesis in plants. Therefore, the transcriptional regulation of some sulfate transporters was determined in this study to clarify the importance of these transporters in leaf and root tissues of Arabidopsis thaliana under toxic B conditions. The expression level of SULTR1;3 was dramatically increased in leaf and root tissues under moderate and severe toxic B conditions, suggesting source-to-sink sulfate translocation under B toxicity. Stable expression levels of SULTR2;1, SULTR2;2, and low SULTR3;5 expression might restrict the sulfate movement into the xylem in leaves. SULTR3;1, SULTR3;2, SULTR3;3, SULTR3;4, SULTR4;1 and SULTR4;2 were induced in root tissues under toxic B conditions, indicating an induction of root-to-shoot sulfate translocation. These results showed that B toxicity might disrupt the homogeneous distribution of sulfate and sulfur-containing compounds in both tissues of A. thaliana. Moreover, we performed in silico analysis of microarray experiments to determine the common differentially expressed genes (DEGs) under B toxicity and sulfur deficiency. Gene ontology, hierarchical clustering, and coexpression network analyses of these DEGs demonstrated the requirement of sulfate transporters under B toxicity. A set of genes involved in sulfur metabolism coexpress with sulfate transporters under B toxicity. To the best of our knowledge, this is the first report focusing on the molecular regulation of sulfate transporters in Arabidopsis thaliana under B toxicity.

Cell-specific transcriptional responses to environmental stimuli are yet to be fully characterized in plants. In this study, we apply single-cell RNA sequencing to Arabidopsis thaliana roots exposed to boron (B) toxicity to characterize the transcription map at cellular resolution and thus, to understand how B toxicity can alter gene expression and development at single cell resolution. Single-cell transcriptomes from protoplasts of more than 2750 Arabidopsis thaliana root cells were obtained. Plotting the single-cell transcriptomes via t-SNE projections yielded six major cell clusters including quiescent cells (QC), endodermis, cortex, columella, trichoblast (root-hair), and root cap. The maximum number of most significantly upregulated genes were determined in columella under 1 mM B and in endodermis under 2 mM B condition. Additionally, the maximum number of most significantly upregulated genes under 3 mM B and 5 mM B conditions was determined in the root cap, implying a critical role against severe B toxicity conditions. We also showed that these upregulated genes are highly correlated with “glutathione metabolism” in columella and “carbon metabolism” in root cap. Taken together, for the first time in the literature, our study provides a gene expression map at single-cell resolution and describes the extent of heterogeneity at the molecular level among populations of different cell types in Arabidopsis root under B toxicity conditions.