Plants employ stomatal closure and reduced growth to avoid water deficiency damage. Reduced levels of the growth-promoting hormone gibberellin (GA) lead to increased tolerance to water deficit, but the underlying mechanism is unknown. Here, we show that the tomato (Solanum lycopersicum) DELLA protein PROCERA (PRO), a negative regulator of GA signaling, acts in guard cells to promote stomatal closure and reduce water loss in response to water deficiency by increasing abscisic acid (ABA) sensitivity. The loss-of-function pro mutant exhibited increased stomatal conductance and rapid wilting under water deficit stress. Transgenic tomato overexpressing constitutively active stable DELLA proteins (S-della) displayed the opposite phenotype. The effects of S-della on stomatal aperture and water loss were strongly suppressed in the ABA-deficient mutant sitiens, indicating that these effects of S-della are ABA dependent. While DELLA had no effect on ABA levels, guard cell ABA responsiveness was increased in S-della and reduced in pro plants compared with the wild type. Expressing S-della under the control of a guard-cell-specific promoter was sufficient to increase stomatal sensitivity to ABA and to reduce water loss under water deficit stress but had no effect on leaf size. This result indicates that DELLA promotes stomatal closure independently of its effect on growth.
Bibliographical noteFunding Information:
This research was supported by a research grant from the U.S. Israel Binational Agriculture Research and Development fund to D.W. and N.O. (Grant US-4813-15C), by The Israel Ministry of Agriculture and Rural Development (Eugene Kandel Knowledge Centers) as part of the Root of the Matter–The root zone knowledge center for leveraging modern agriculture to D.W., and by The I-CORE Program of the Planning and Budgeting Committee and The Israel Science Foundation (Grant757/12) to D.W. and A.A. We thank NaomiOriand Menachem Moshilion for their valuable suggestions.