OSCA1 is an osmotic specific sensor: a method to distinguish Ca²⁺‐mediated osmotic and ionic perception

Abstract

Summary Genetic mutants defective in stimulus‐induced Ca2+ increases have been gradually isolated, allowing the identification of cell‐surface sensors/receptors, such as the osmosensor OSCA1. However, determining the Ca2+‐signaling specificity to various stimuli in these mutants remains a challenge. For instance, less is known about the exact selectivity between osmotic and ionic stresses in the osca1 mutant. Here, we have developed a method to distinguish the osmotic and ionic effects by analyzing Ca2+ increases, and demonstrated that osca1 is impaired primarily in Ca2+ increases induced by the osmotic but not ionic stress. We recorded Ca2+ increases induced by sorbitol (osmotic effect, OE) and NaCl/CaCl2 (OE + ionic effect, IE) in Arabidopsis wild‐type and osca1 seedlings. We assumed the NaCl/CaCl2 total effect (TE) = OE + IE, then developed procedures for Ca2+ imaging, image analysis and mathematic fitting/modeling, and found osca1 defects mainly in OE. The osmotic specificity of osca1 suggests that osmotic and ionic perceptions are independent. The precise estimation of these two stress effects is applicable not only to new Ca2+‐signaling mutants with distinct stimulus specificity but also the complex Ca2+ signaling crosstalk among multiple concurrent stresses that occur naturally, and will enable us to specifically fine tune multiple signal pathways to improve crop yields.

Comparative analysis of stress-induced calcium signals in the crop species barley and the model plant Arabidopsis thaliana

“…In Arabidopsis, Ca 2+ elevations in response to hyperosmotic stress depend on OSCA1, which operates as an osmosensor in the root and guard cell plasma membrane [ 52 , 53 ]. In addition, Ca 2+ channel-forming annexins activated by hydroxyl radicals may play a role under osmotic and salt stress conditions [ 54 ], a mechanism that has also been suggested for barley [ 50 ].…”

Abiotic Stress in Crop Production

“…The signaling pathway employing the Ca 2+ channel pattern along root cells, endoplasmic reticulum-localized type 2A Ca 2+ -ATPase (ECA1), and MIZU-KUSSEY1 (MIZ1), have been shown to play an important role in root hydrotropism in the model plant Arabidopsis [ 111 ], although the complete molecular mechanism, including the sensor, remains unclear. Part of the mechanism could be hyperosmolality-gated Ca 2+ -permeable ion channels such as OSCA1 that can modulate Ca 2+ concentration in response to osmotic stress [ 112 ] and distinguish between osmotic and ionic stress [ 113 ]. Recently, the role of plasma membrane-localized OSCA1.1 in root bending and hydrotropism has also been confirmed [ 114 ].…”

How do plants maintain pH and ion homeostasis under saline-alkali stress?

“…The osca1 mutant shows impaired Ca 2+ signaling in response to osmotic stress but not salt stress [16]. Recent mathematical fitting/modeling analysis in wild-type Arabidopsis and theosca1 mutant revealed that OSCA1 is responsible for the increase of [Ca 2+ ] cyt induced by osmotic stress rather than ionic stress [17].…”

“…Different from animals, plants might sense salt through a multicomponent ion channel complex rather than through simple ion channels. In addition, this ion channel complex might not be controlled directly by salt [17,24,27]. Identifying the salt sensor remains a problem that scientists are eager to solve.…”