A Guard-Cell-Specific MYB Transcription Factor Regulates Stomatal Movements and Plant Drought Tolerance

Abstract

Stomatal pores located on the plant epidermis regulate CO(2) uptake for photosynthesis and the loss of water by transpiration. The opening and closing of the pore is mediated by turgor-driven volume changes of two surrounding guard cells. These highly specialized cells integrate internal signals and environmental stimuli to modulate stomatal aperture for plant survival under diverse conditions. Modulation of transcription and mRNA processing play important roles in controlling guard-cell activity, although the details of these levels of regulation remain mostly unknown. Here we report the characterization of AtMYB60, a R2R3-MYB gene of Arabidopsis, as the first transcription factor involved in the regulation of stomatal movements. AtMYB60 is specifically expressed in guard cells, and its expression is negatively modulated during drought. A null mutation in AtMYB60 results in the constitutive reduction of stomatal opening and in decreased wilting under water stress conditions. Transcript levels of a limited number of genes are altered in the mutant, and many of these genes are involved in the plant response to stress. Our data indicate that AtMYB60 is a transcriptional modulator of physiological responses in guard cells and open new possibilities to engineering stomatal activity to help plants survive desiccation.

Overexpression of AtMYB44 Enhances Stomatal Closure to Confer Abiotic Stress Tolerance in Transgenic Arabidopsis

“…In addition, the Arabidopsis mutant hos10-1 (conferring high expression of osmotically responsive genes) exhibits altered expression of ABA-responsive genes, showing dramatically reduced capacity for cold acclimation and hypersensitivity to dehydration and salinity . As reported recently, AtMYB60 is specifically expressed in guard cells and involved in light-induced opening of stomata (Cominelli et al, 2005), whereas AtMYB61 is expressed under conditions necessary for dark-induced stomatal closure (Liang et al, 2005).…”

“…For instance, overexpression of AtMYB61 (Liang et al, 2005), which controls dark-induced stomatal closure, resulted in smaller stomatal apertures in transgenic Arabidopsis. Mutations on AtMYB60, which controls stomatal opening (Cominelli et al, 2005), OST1, which encodes a protein kinase involved in ABAmediated stomatal closure (Xie et al, 2006), and HT1, which encodes a kinase involved in stomatal movements in response to CO 2 (Hashimoto et al, 2006), also resulted in smaller stomatal apertures, respectively. Therefore, overexpression or mutation of the genes involved directly or indirectly in structural movements of the stomata might affect morphology of the guard cells in transgenic plants.…”

Stomatal Size, Speed, and Responsiveness Impact on Photosynthesis and Water Use Efficiency

“…For example, transcriptional analysis of guard cells from epidermal fragments (Wang et al, 2012) or microdisection of individual guard cells (Gandotra et al, 2013), along with single-cell metabolic profiling (Burrell et al, 2007), have greatly assisted in our understanding of the metabolic signaling and response pathways within guard cells. The identification of highly specific guard cell promoters (Müller-Röber et al, 1994;Cominelli et al, 2005) and transcription factors (Cominelli et al, 2010;Yoo et al, 2010), the production of guard cell enhancer trap lines (Gardner et al, 2009), and the ability to induce transient expression in guard cells (Rusconi et al, 2013) open up new exciting potential approaches to not only fully understand signaling and transduction pathways in guard cells but also to provide us with the tools to manipulate guard cell metabolism in order to improve plant WUE. Such tools have greatly improved our understanding of the molecular networks that control guard cell perception of and response to internal and external environmental cues and have provided possible candidates for manipulation (Galbiati et al, 2008;Rusconi et al, 2013).…”

MYB transcription factor genes as regulators for plant responses: an overview

“…AtMYB60 and AtMYB96 acted through the ABA signaling cascade to regulate stomatal movement (Cominelli et al 2005), and drought stress and disease resistance Seo and Park 2010) respectively. The transcriptional activation of cuticular wax biosynthesis by MYB96 contributed to drought resistance in Arabidopsis thaliana (Seo et al 2011).…”