The SlWRKY81 transcription factor inhibits stomatal closure by attenuating nitric oxide accumulation in the guard cells of tomato under drought

Abstract

The WRKY transcription factors (TFs) play multifaceted roles in plant growth, development, and stress response. Previously, we found that SlWRKY81 negatively regulates tomato tolerance to drought; however, the mechanisms of stomatal regulation in response to drought remain largely unclear. Here, we showed that droughtinduced upregulation in the SlWRKY81 transcripts induced photoinhibition and reduced the net photosynthetic rate in tomato leaves. However, silencing SlWRKY81 alleviated those inhibitions and minimized the drought-induced damage. A timecourse of water loss showed that SlWRKY81 silencing significantly and consistently reduced leaf water loss, suggesting a role for SlWRKY81 in stomatal movement. Further analysis using light microscopy revealed that SlWRKY81 silencing significantly decreased stomatal aperture and increased the ratio of length to width of stomata under drought. Both biochemical assay and confocal laser scanning microscopy demonstrated that drought-induced upregulation in SlWRKY81 expression inhibited the nitric oxide (NO) accumulation in the guard cells, which was attributed to the simultaneous declines in the activity of nitrate reductase (NR) and NR expression in tomato leaves. The inspection of 3-kb sequences upstream of the predicted transcriptional start site of the NR identified three copies of the core W-box (TTGACC/T) sequence in the promoter region, indicating possible targets of SlWRKY81. Taken together, these data suggest that SlWRKY81 potentially represses NR transcription and thus reduces NO accumulation to attenuate stomatal closure and subsequent drought tolerance. These findings provide an improved understanding of the mechanism of WRKY-induced regulation of stomatal closure, which can be exploited in the future to enhance drought tolerance in crops. | INTRODUCTIONPlant growth, development, and productivity primarily depend on water availability. Deficit water supply results in drought that remarkably affects multiple plant physiological processes, leading to yield losses (de Vries et al., 2020). Drought is a major abiotic stress, limiting crop production around the world (Bartlett et al.,

Melatonin Pretreatment Confers Heat Tolerance and Repression of Heat-Induced Senescence in Tomato Through the Modulation of ABA- and GA-Mediated Pathways

“…Two essential fluorescence attributes net photosynthetic rate (P n ) and stomatal conductance (G s ), were measured with a portable photosynthesis system (Li-6400; LI-COR, Inc., Lincoln, NE, United States) from 10.00 am to 11.00 am. The cuvette conditions were maintained as follows: 25 • C temperature, 70% relative humidity, 800 µmol photons m −2 s −1 PPFD (photosynthetic photon flux density), and 380 ± 10 µmol mol −1 external CO 2 concentration (Ahammed et al, 2020a;Hasan et al, 2020).…”

Molecular Mechanisms of Nitric Oxide (NO) Signaling and Reactive Oxygen Species (ROS) Homeostasis during Abiotic Stresses in Plants

“…Overexpression of SlWRKY8, which belongs to the WRKY transcription factor superfamily, increases drought tolerance in tomato [101]. In contrast, SlWRKY81 negatively regulates tomato drought tolerance by repressing NR activity, leading to reduced NO accumulation and eventually to reduced stomatal closure, which in turn increases water loss [102]. Silencing of SlWRKY81 resulted in increased NO accumulation in guard cells due to increased NR expression, leading to more efficient stomatal closure and reduced water loss [102].…”

Dew absorption by leaf trichomes in Caragana korshinskii: An alternative water acquisition strategy for withstanding drought in arid environments

“…In arid environments, plants consistently face environmental challenges, such as water scarcity (Brodribb et al, 2020; Choat et al, 2012; Yao et al, 2021) Therefore, plants have evolved diverse coping strategies to adapt to these conditions, including developing deeper root architecture to maximize water absorption from soil (Gibbens & Lenz, 2001), having smaller leaf surface area to minimize water loss through transpiration and exhibiting rapid stomatal closure (Ahammed, Li, Mao, et al, 2020; Ahammed, Li, Wan, et al, 2020; Ahammed, Li, Yang, et al, 2020; Li et al, 2019; Li et al, 2020; Yao et al, 2020). Other structural modifications in the form of epidermal appendages designed to collect atmospheric water, such as the unique conical spines on cactus stems, the awns of desert mosses (Ju et al, 2012; Pan et al, 2016), and the leaf trichomes in numerous xeromorphic plant species (Huttunen et al, 2010; Ning et al, 2016; Schreel et al, 2020).…”