Guard cell-specific expression of AtTOR enhances drought tolerance and water use efficiency in Arabidopsis by reducing transpirational water loss while maintaining or improving photosynthetic performance through modulation of stomatal function and ABA-related signaling pathways.

Keywords: Arabidopsis, Drought resistance, Ectopic expression, Guard cell, Leaf conductance, Photosynthesis, TOR, Transpiration, Water use efficiency

Growth and development in eukaryotes are tightly regulated by TOR kinase, a conserved signaling hub that integrates cues from energy status, nutrients, and environmental stress. In plants, TOR has emerged as a key player not only in promoting growth but also in modulating stress responses through crosstalk with hormonal pathways like abscisic acid (ABA). Yet, its role in optimizing long-term water use efficiency (WUE) during drought has remained poorly understood. In a recent collaborative study, scientists from the University of Saskatchewan, National Research Council Canada, the Chinese Academy of Agricultural Sciences, and INIFAP-Mexico revealed that overexpressing Arabidopsis TOR (AtTOR) either constitutively or specifically in guard cells significantly enhances drought resilience, biomass accumulation, and WUE. Remarkably, even when TOR expression was restricted to guard cells—where stomatal apertures and water loss are regulated—plants maintained or increased photosynthetic rates despite reduced stomatal conductance. This indicates that TOR-driven improvements in photosynthetic efficiency can offset reduced CO₂ diffusion, likely via upregulation of chlorophyll content and carbon assimilation pathways.

Transcriptomic analysis supported this physiological shift, identifying differentially expressed genes involved in ABA signaling, drought adaptation, and stomatal development, including CYP707A1 and CYP707A3, which are linked to ABA metabolism. Compared to other transgenic strategies for improving WUE—such as modifying ABA receptor levels or stomatal patterning—the AtTOR approach achieved much greater efficiency gains (up to 160% under drought and 110% during recovery), without compromising growth or survival. These results suggest that localized TOR manipulation in guard cells offers a powerful and precise means of improving drought tolerance and WUE. The study not only highlights TOR’s broader regulatory role in integrating metabolic and stress signals but also lays the foundation for next-generation crop improvement strategies through cell-type-specific gene expression or genome editing.

SorghumBase examples: 

Figure 1: The taxonomic distribution of AtTOR (AT1G50030) Target of rapamycin in SorghumBase highlights its evolutionary conservation within Sorghum bicolor (SORBI_3009G109200), closely related grasses (Oryza sativa Os05g0235300 and Maize Zm00001eb285840). The phylogenetic tree (above) illustrates these evolutionary relationships, displaying a multi-species sequence alignment with color-coded blocks representing conserved sequence regions. 
Figure 2: Phylogenetic tree in the Homology tab of the SorghumBase search interface illustrating the relationships between SORBI_3009G109200 (similar to target of rapamycin) genes across species and alleles in assembled Sorghum genomes, as determined using Ensembl Compara, a comparative genomics tool available on SorghumBase. It has a 94% identity with OsTOR. There are 211 homologs that includes 52 orthologs and 4 paralogs.
Figure 3: Location tab of the SorghumBase search interface of SORBI_3009G109200 (similar to target of rapamycin) gene shows that this gene is located on chromosome 9: 44026411-44064647.
Figure 4: Sequence tab of the SorghumBase search interface of SORBI_3009G109200 (similar to target of rapamycin) gene provides the genomic, transcript and peptide sequence. The figure displays the peptide sequence of SORBI_3009G109200 (similar to the target of rapamycin) gene. 
Reference:

Liu L, Gao P, Sheng H, Bakshi A, Schneider D, Xiang D, Babic V, Ren M, Burbridge C, Nguyen H, Wang S, Armenta-Medina A, Mora-Macias J, Sharpe A, Pozniak C, Magalhaes J, Datla R, Kochian L. Guard cell and whole plant expression of AtTOR improves performance under drought and enhances water use efficiency. J Biol Chem. 2025 May 13;301(6):110220. PMID: 40374165. doi: 10.1016/j.jbc.2025.110220. Read more

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Guard Cell-Targeted TOR Expression Enhances Drought Tolerance and Water Use Efficiency in Arabidopsis

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