The Ca2+ Sensor Calcineurin B-Like Protein 10 in Plants: Emerging New Crucial Roles for Plant Abiotic Stress Tolerance.

Francisco B Flores,Felix A Plasencia,Yanira Estrada,Isabel Egea,Ana Ortíz-Atienza,Rafael Lozano

doi:10.3389/fpls.2020.599944

Abstract

Ca2+ is a second messenger that mediates plant responses to abiotic stress; Ca2+ signals need to be decoded by Ca2+ sensors that translate the signal into physiological, metabolic, and molecular responses. Recent research regarding the Ca2+ sensor CALCINEURIN B-LIKE PROTEIN 10 (CBL10) has resulted in important advances in understanding the function of this signaling component during abiotic stress tolerance. Under saline conditions, CBL10 function was initially understood to be linked to regulation of Na+ homeostasis, protecting plant shoots from salt stress. During this process, CBL10 interacts with the CBL-interacting protein kinase 24 (CIPK24, SOS2), this interaction being localized at both the plasma and vacuolar (tonoplast) membranes. Interestingly, recent studies have exposed that CBL10 is a regulator not only of Na+ homeostasis but also of Ca2+ under salt stress, regulating Ca2+ fluxes in vacuoles, and also at the plasma membrane. This review summarizes new research regarding functions of CBL10 in plant stress tolerance, predominantly salt stress, as this is the most commonly studied abiotic stress associated with the function of this regulator. Special focus has been placed on some aspects that are still unclear. We also pay particular attention on the proven versatility of CBL10 to activate (in a CIPK-dependent manner) or repress (by direct interaction) downstream targets, in different subcellular locations. These in turn appear to be the link through which CBL10 could be a key master regulator of stress signaling in plants and also a crucial participant in fruit development and quality, as disruption of CBL10 results in inadequate Ca2+ partitioning in plants and fruit. New emerging roles associated with other abiotic stresses in addition to salt stress, such as drought, flooding, and K+ deficiency, are also addressed in this review. Finally, we provide an outline of recent advances in identification of potential targets of CBL10, as CBL10/CIPKs complexes and as CBL10 direct interactions. The aim is to showcase new research regarding this master regulator of abiotic stress tolerance that may be essential to the maintenance of crop productivity under abiotic stress. This is particularly pertinent when considering the scenario of a projected increase in extreme environmental conditions due to climate change.

Highlights

CBL-CBL-interacting protein kinases (CIPKs), A VERSATILE STRESS RESPONSE MECHANISM MEDIATED BY Ca2+ IN PLANTSPlants have evolved a complex system to interact with the environment during evolution, which is able to perceive, transduce, and trigger responses to stresses at molecular, cellular, and physiological levels
Such an expression pattern resulted in a reduced upload of Na+ from the xylem, allowing toxic ions to reach the shoot apex, inducing its collapse and subsequent plant death (Egea et al, 2018). These findings reveal that SlCBL10 is required for the regulation of Na+ homeostasis through the activity of gene products involved in the compartmentalization of Na+ into vacuoles (Figure 1); this is in agreement with the first hypothesis postulated by Kim et al (2007), and it is supported by several studies that have established the subcellular localization of CALCINEURIN B-LIKE PROTEIN 10 (CBL10)–SOS2 at the tonoplast (Waadt et al, 2008; Tang et al, 2014)
Research on the Ca2+ sensor CBL10 has yielded important advances in the understanding of functions of this signaling component in different facets of plant development and stress tolerance. Results from these studies seem to point to CBL10 as a key master regulator of stress in plants. This hypothesis is supported by the demonstrated ability of CBL10 to interact with diverse CIPKs, downward activating specific targets, as well as through the demonstrated possibility of its direct interaction with targets repressing their activity, in such a way that opens the possibility of modulating the response to a particular stressor (Figure 2)

Summary

Introduction

CBL-CIPK, A VERSATILE STRESS RESPONSE MECHANISM MEDIATED BY Ca2+ IN PLANTSPlants have evolved a complex system to interact with the environment during evolution, which is able to perceive, transduce, and trigger responses to stresses at molecular, cellular, and physiological levels. Our study demonstrated that the transcriptional activity of SlCBL10 in this specific tissue is critically involved in the adaptive response of tomato plants to salt stress as it protects shoot apical meristems and growing tissues from physiological damage caused by salinity.

Results

Conclusion