Light-induced stomatal opening is affected by the guard cell protein kinase APK1b.

Nagat S. Elhaddad,Lee Hunt,Jennifer Sloan,Julie E. Gray,Carl Ng

doi:10.1371/journal.pone.0097161

Nagat S. Elhaddad, Lee Hunt + Show 3 more

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https://doi.org/10.1371/journal.pone.0097161

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Journal: PloS one	Publication Date: May 14, 2014
Citations: 42	License type: CC BY 4.0

Affiliation: University of Sheffield

Abstract

Guard cells allow land plants to survive under restricted or fluctuating water availability. They control the exchange of gases between the external environment and the interior of the plant by regulating the aperture of stomatal pores in response to environmental stimuli such as light intensity, and are important regulators of plant productivity. Their turgor driven movements are under the control of a signalling network that is not yet fully characterised. A reporter gene fusion confirmed that the Arabidopsis APK1b protein kinase gene is predominantly expressed in guard cells. Infrared gas analysis and stomatal aperture measurements indicated that plants lacking APK1b are impaired in their ability to open their stomata on exposure to light, but retain the ability to adjust their stomatal apertures in response to darkness, abscisic acid or lack of carbon dioxide. Stomatal opening was not specifically impaired in response to either red or blue light as both of these stimuli caused some increase in stomatal conductance. Consistent with the reduction in maximum stomatal conductance, the relative water content of plants lacking APK1b was significantly increased under both well-watered and drought conditions. We conclude that APK1b is required for full stomatal opening in the light but is not required for stomatal closure.

Highlights

The activity of several protein kinases has been shown to be important in mediating stomatal responses to environmental stimuli, including light intensity, pathogens, atmospheric carbon dioxide concentration and the drought hormone abscisic acid (ABA)
Well-characterised Arabidopsis guard cell kinases include HIGH LEAF TEMPERATURE (HT1), OPEN STOMATA 1 (OST1), phototropins PHOT1 PHOT2, PKS5, BLUE LIGHT SIGNALLING 1 (BLUS1) and calcium-dependent protein kinases CPK 3, 6 21 and 23, which are required for stomatal closure responses to atmospheric CO2 concentration [1,2] and abscisic acid (ABA) [3,4,5] and for the stomatal opening response to blue light [6,7,8]
A number of transcriptomics experiments have suggested that the protein kinase encoded by APK1b is highly expressed in guard cells relative to other cell types [11,15,16]

Summary

Introduction

The activity of several protein kinases has been shown to be important in mediating stomatal responses to environmental stimuli, including light intensity, pathogens, atmospheric carbon dioxide concentration and the drought hormone abscisic acid (ABA). The encoded proteins phosphorylate tyrosine, serine and threonine residues in vitro [10] but the nature of their in vivo substrate(s) have not been investigated Beyond their kinase activity their function is unknown, transcriptomics experiments suggest that APK1a and APK1b are predominantly expressed in guard cells [11] (Figure S1). Homology searching suggests that these genes are members of the receptor-like cytoplasmic kinase VII subfamily [12]. The role of this subfamily of kinases has not previously been investigated in stomatal responses. APK1a and APK1b have closest homology to Botrytis Induced Kinase 1 (BIK1), lack of which results in severe susceptibility to necrotrophic fungal pathogens but does not impair responses to the bacterial pathogen Pseudomonas syringae [14]

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Conclusion