Metabolic engineering of stomatal precursor cells enhances photosynthetic water‐use efficiency and vegetative growth under water‐deficit conditions in <i>Arabidopsis thaliana</i>

Stomata are epidermal pores that control the exchange of gaseous CO₂ and H₂O between plants and their environment. Modulating stomatal density can alter this exchange and thus presents a viable target for engineering improved crop productivity and climate resilience. Here, we show that stomatal density in Arabidopsis thaliana can be decreased by the expression of a water-forming NAD(P)H oxidase targeted to stomatal precursor cells. We demonstrate that this reduction in stomatal density occurs irrespective of whether the expressed enzyme is localized to the cytosol, chloroplast stroma or chloroplast intermembrane space of these cells. We also reveal that this decrease in stomatal density occurs in the absence of any measurable impact on the efficiency and thermal sensitivity of photosynthesis, or on stomatal dynamics. Consequently, overexpression plants exhibit a higher intrinsic water-use efficiency due to an increase in CO₂ fixed per unit water transpired. Finally, we demonstrate that this enhanced water-use efficiency translates to an improvement in vegetative growth and biomass accumulation under water-deficit conditions. Together, these results thus provide a novel approach for enhancing plant productivity through metabolic engineering of stomatal density.