The Tomato DELLA Protein PROCERA Acts in Guard Cells to Promote Stomatal Closure

Abstract

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 () 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 mutant exhibited increased stomatal conductance and rapid wilting under water deficit stress. Transgenic tomato overexpressing constitutively active stable DELLA proteins (S-) displayed the opposite phenotype. The effects of S- on stomatal aperture and water loss were strongly suppressed in the ABA-deficient mutant , indicating that these effects of S- are ABA dependent. While DELLA had no effect on ABA levels, guard cell ABA responsiveness was increased in S- and reduced in plants compared with the wild type. Expressing S- 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.

Mutations in the tomato gibberellin receptors suppresses xylem proliferation and reduces water loss under water-deficit conditions

“…Previously we showed that all double mutants exhibit reduced whole plant transpiration (Illouz-Eliaz et al, 2019). Here we examined whole-plant transpiration in irrigated M82 and gid1a mutant plants grown in a greenhouse using an array of load cells (lysimeters) which simultaneously followed the daily weight loss of each plant (Nir et al, 2017). Daily transpiration, transpiration rate and whole canopy conductance of gid1a were significantly lower than that of M82 (Fig.…”

“…To remove residues of buffer and cell particles, the tubes were centrifuged at 4°C for 5 min at 2200 rpm. Samples of digested epidermal strips were stained with neutral red, and cell vitality was examined microscopically (Nir et al ., 2017).…”

“…Inhibition of GA activity in tomato by overexpressing the Arabidopsis GA METHYL TRANSFERASE 1 ( AtGAMT1 ) gene or the gain-of-function stable DELLA mutant gene proΔ17 , reduced whole plant transpiration and improved resistance to drought (Nir et al ., 2014; Nir et al ., 2017). Several possible mechanisms for this stress tolerance were suggested, including indirect effects on transpiration due to reduced plant size (Magome et al ., 2008; Achard et al ., 2006) and direct effect on transpiration, due to increased response to ABA in guard cell and rapid stomatal closure (Nir et al, 2017). Low GA activity also led to the activation of various stress-related genes (Wang et al ., 2008; Tuna et al ., 2008) and the accumulation of osmolytes (Omena-Garcia et al, 2019).…”

Guarding the Gates: How PROCERA Helps Keep Tomato Plants from Wilting

“…By combining rigorous physiological studies in tomato with genetic/misexpression analysis, Nir et al (2017) were able to do just that. Conveniently, unlike Arabidopsis thaliana, which contains five DELLA genes, tomato has only one, PROCERA (PRO).…”

“…Wild-type (M82), sit, 35S pro :proΔ17 (proΔ17), and 35S pro :proD17 plants in the sit background (proΔ17 sit) grown under a normal irrigation regime (1 irrigation) or without irrigation for 7 d. After 7 d without irrigation, the plants were rehydrated and recovery was assessed 10 d later. (Reprinted from Nir et al [2017], Figure 4A.) OPEN Articles can be viewed without a subscription.…”