Calcium Efflux Systems in Stress Signaling and Adaptation in Plants

Abstract

Transient cytosolic calcium ([Ca2+]cyt) elevation is an ubiquitous denominator of the signaling network when plants are exposed to literally every known abiotic and biotic stress. These stress-induced [Ca2+]cyt elevations vary in magnitude, frequency, and shape, depending on the severity of the stress as well the type of stress experienced. This creates a unique stress-specific calcium “signature” that is then decoded by signal transduction networks. While most published papers have been focused predominantly on the role of Ca2+ influx mechanisms to shaping [Ca2+]cyt signatures, restoration of the basal [Ca2+]cyt levels is impossible without both cytosolic Ca2+ buffering and efficient Ca2+ efflux mechanisms removing excess Ca2+ from cytosol, to reload Ca2+ stores and to terminate Ca2+ signaling. This is the topic of the current review. The molecular identity of two major types of Ca2+ efflux systems, Ca2+-ATPase pumps and Ca2+/H+ exchangers, is described, and their regulatory modes are analyzed in detail. The spatial and temporal organization of calcium signaling networks is described, and the importance of existence of intracellular calcium microdomains is discussed. Experimental evidence for the role of Ca2+ efflux systems in plant responses to a range of abiotic and biotic factors is summarized. Contribution of Ca2+-ATPase pumps and Ca2+/H+ exchangers in shaping [Ca2+]cyt signatures is then modeled by using a four-component model (plasma- and endo-membrane-based Ca2+-permeable channels and efflux systems) taking into account the cytosolic Ca2+ buffering. It is concluded that physiologically relevant variations in the activity of Ca2+-ATPase pumps and Ca2+/H+ exchangers are sufficient to fully describe all the reported experimental evidence and determine the shape of [Ca2+]cyt signatures in response to environmental stimuli, emphasizing the crucial role these active efflux systems play in plant adaptive responses to environment.

The Pseudomonas aeruginosa PAO1 Two-Component Regulator CarSR Regulates Calcium Homeostasis and Calcium-Induced Virulence Factor Production through Its Regulatory Targets CarO and CarP

“…As a plant and human pathogen, P. aeruginosa may be exposed to lower but also varying Ca 2ϩ levels. For example, in plants, the Ca 2ϩ concentration ranges from 0.01 to 1 mM in extracellular spaces (9) and from 1 to 10 mM in apoplasts (10). In a human body, Ca 2ϩ levels may reach about 1 to 2 mM in extracellular fluids and saliva (11) (12) and 5 mM in blood (13) and human milk (14).…”

Effect of preparations Methyure and Ivine on Са(2+)-ATPases activity in plasma and vacuolar membrane of corn seedling roots under salt stress conditions

“…Such an effect of salt exposure on activity of Ca 2+ -АТPases in these membrane was also shown on other cultures. The given Ca 2+ -АТPases play great role in ecologic plasticity of plants that was demonstrated at the early varieties of rice, tomatoes, radish and corn [6][7][8][9].…”

“…The presence of Na + causes temporary accu mulation of the both subtypes of Са 2+ -АТPases that indicates their role in adaptation to salinity condi tions [6,[8][9][10].…”

“…The increase of Ca 2+ concentration in cytoplasm activates signals transduction through SOSsystem that results in removal of Na + [5]. Calcium homeostasis in cytoplasm under sa linity conditions is maintained by Ca 2+ -АТРases and Ca 2+ /Н + antiporters, which function in various cell membrane structures, the latter being included at high concentrations [6]. Ca 2+ -АТРases of the plasma and vacuolar membrane play the important role in formation of cell response to different stimuli, in cluding salting conditions characterized by con tinuous action.…”

“…Ca 2+ -ATPase of plant membrane is represented by two subtypes: Ca 2+ -АТРase ІІА and Ca 2+ -АТРase ІІВ, the latter displaying sensiti vity to calmodulin. They are simi lar to Ca 2+ -АТРase of animal cells as to their struc ture and membrane localization [6][7][8][9][10][11][12].…”