Increasing water‐use efficiency directly through genetic manipulation of stomatal density

Summary Improvement in crop water‐use efficiency ( WUE ) is a critical priority for regions facing increased drought or diminished groundwater resources. Despite new tools for the manipulation of stomatal development, the engineering of plants with high WUE remains a challenge. We used Arabidopsis epidermal patterning factor ( EPF ) mutants exhibiting altered stomatal density to test whether WUE could be improved directly by manipulation of the genes controlling stomatal density. Specifically, we tested whether constitutive overexpression of EPF 2 reduced stomatal density and maximum stomatal conductance ( g w(max) ) sufficiently to increase WUE . We found that a reduction in g w(max) via reduced stomatal density in EPF 2 ‐overexpressing plants ( EPF 2 OE ) increased both instantaneous and long‐term WUE without altering significantly the photosynthetic capacity. Conversely, plants lacking both EPF 1 and EPF 2 expression ( epf1epf2 ) exhibited higher stomatal density, higher g w(max) and lower instantaneous WUE , as well as lower (but not significantly so) long‐term WUE . Targeted genetic modification of stomatal conductance, such as in EPF 2 OE , is a viable approach for the engineering of higher WUE in crops, particularly in future high‐carbon‐dioxide ( CO 2 ) atmospheres.