Calcium channels and transporters: Roles in response to biotic and abiotic stresses

Abstract

Calcium (Ca²⁺) serves as a ubiquitous second messenger by mediating various signaling pathways and responding to numerous environmental conditions in eukaryotes. Therefore, plant cells have developed complex mechanisms of Ca²⁺ communication across the membrane, receiving the message from their surroundings and transducing the information into cells and organelles. A wide range of biotic and abiotic stresses cause the increase in [Ca²⁺]_cyt as a result of the Ca²⁺ influx permitted by membrane-localized Ca²⁺ permeable cation channels such as CYCLIC NUCLEOTIDE-GATE CHANNELs (CNGCs), and voltage-dependent HYPERPOLARIZATION-ACTIVATED CALCIUM²⁺ PERMEABLE CHANNELs (HACCs), as well as GLUTAMATE RECEPTOR-LIKE RECEPTORs (GLRs) and TWO-PORE CHANNELs (TPCs). Recently, resistosomes formed by some NUCLEOTIDE-BINDING LEUCINE-RICH REPEAT RECEPTORs (NLRs) are also proposed as a new type of Ca²⁺ permeable cation channels. On the contrary, some Ca²⁺ transporting membrane proteins, mainly Ca²⁺-ATPase and Ca²⁺/H⁺ exchangers, are involved in Ca²⁺ efflux for removal of the excessive [Ca²⁺]_cyt in order to maintain the Ca²⁺ homeostasis in cells. The Ca²⁺ efflux mechanisms mediate the wide ranges of cellular activities responding to external and internal stimuli. In this review, we will summarize and discuss the recent discoveries of various membrane proteins involved in Ca²⁺ influx and efflux which play an essential role in fine-tuning the processing of information for plant responses to abiotic and biotic stresses.

Keywords: Ca2+ efflux; Ca2+ influx; abiotic stress; biotic stress; calcium; channels; transporters.

Figure 1

Arabidopsis and rice Ca²⁺ channels and transporters involved in diverse stresses. (A) Schematic summary of Arabidopsis and rice Ca²⁺ channels involved in abiotic stresses. The Ca²⁺ channels whose function were validated in Arabidopsis and rice are shown. Cold/freezing, metal, salt, hypoxia, wound, and heat stresses are depicted. When two channels create a complex and function as one unit, they are marked together. (B) Schematic summary of Arabidopsis and rice Ca²⁺ channels involved in biotic stress and cell death. The calcium channels whose function were validated in Arabidopsis and rice are shown. Transporters belonging to the same family are marked with the same geometric shapes. When two or more channels create a complex and function as one unit, they are marked together.