CML20, an Arabidopsis Calmodulin-like Protein, Negatively Regulates Guard Cell ABA Signaling and Drought Stress Tolerance.

Xiaomeng Wu,Chunlong Li,Biswa R Acharya,Huiping Liu,Zhu Qiao,Wei Zhang

doi:10.3389/fpls.2017.00824

Abstract

Guard cells shrink in response to drought and abscisic acid (ABA), which is caused by efflux of ions that in turn reduces stomatal aperture and improves the plant’s ability to retain moisture. Cytosolic free calcium is an essential secondary messenger in guard cell ABA signaling, but the details of this regulatory pathway remain sketchy. Here, the calmodulin-like protein CML20, which has four EF-hand domains and calcium-binding activity in vitro, was found to be a negative regulator of ABA-induced stomatal movement in Arabidopsis. The guard cells of cml20 loss-of-function mutant plants were hypersensitive to both ABA-activated S-type anion currents, and ABA inhibited inward K+ currents than those of wild type. Additional, due to smaller stomatal aperture, cml20 showed less water loss from the leaves than wild type. These phenotypes of CML20 overexpressing plants contrasted with wild type in the opposite direction. In the cml20 mutant, the transcripts of stress responsive genes, such as MYB2, RAB18, ERD10, COR47, and RD29A were up-regulated in response to drought and ABA, while down-regulated of APX2 transcription and higher reactive oxygen species (ROS) accumulation. These observations support the CML20, a functional Ca2+ sensor, is a negative regulator in guard cell ABA signaling.

Highlights

Drought stress represents one of the most important constraints on crop productivity
Given that CML20 was clearly up-regulated by abscisic acid (ABA) in the guard cells, the response of cml20 guard cells was of interest to study its role in ABA signaling
The results indicated that cml20 stomata were hypersensitive to both ABApromoted stomatal closure as well as the ABA-inhibited stomatal opening, and to minimize the water loss to increase the plant drought tolerance

Summary

Introduction

Drought stress represents one of the most important constraints on crop productivity. Stomatal closure is a key early plant response to drought stress (Verslues et al, 2006), a process which is controlled by the turgor of the pair of guard cells surrounding each stoma (Kwak et al, 2008). Drought stress promotes the tissue content of the phytohormone abscisic acid (ABA), which acts as a prominent regulator of stomatal movement through its effect on ion channel activity (Schroeder et al, 2001). The supply of exogenous Ca2+ can induce stomatal closure and can oscillate the CML20 Regulates Plant Drought Response concentration of cytosolic Ca2+ (McAinsh et al, 1995; Pei et al, 2000; Siegel et al, 2009). Certain stimuli that induce stomatal opening may act to enhance the concentration of cytosolic Ca2+ (Kenichiro et al, 1992; Cousson and Vavasseur, 1998)

Methods

Results

Conclusion