Abstract
Calcium-permeable channels underpin elevations of free calcium that encode specific signals in stress adaptation, development and immunity. Identifying the genes encoding these channels remains a central goal of plant signalling research. Evidence now suggests that members of the plant annexin family function as unconventional calcium-permeable channels, with roles in development and stress signalling. Arabidopsis annexin 1 mediates a plasma membrane calcium-permeable conductance in roots that is activated by reactive oxygen species. Recombinant annexin 1 forms a very similar conductance in planar lipid bilayers, indicating that this protein could facilitate the in vivo conductance directly. The annexin 1 mutant is impaired in salinity-induced calcium signalling. Protein–protein interactions, post-translational modification and dynamic association with membranes could all influence annexin-mediated calcium signalling and are reviewed here. The prospect of annexins playing roles in calcium signalling events in symbiosis and immunity are considered.
Highlights
IntroductionCalcium influx to the cytosol (from the apoplast or from organellar stores) is central to elevation of cytosolic free Ca2+ ([Ca2+]cyt) as a second messenger in developmental, stress and immune signalling [1]
Calcium influx to the cytosol is central to elevation of cytosolic free Ca2+ ([Ca2+]cyt) as a second messenger in developmental, stress and immune signalling [1]
At the vacuole of Arabidopsis thaliana and rice, TPC1 (Two Pore Channel 1) would be capable of releasing Ca2+ to the cytosol [4], modelling studies suggest that it would not be a component of guard cell Ca2+ signalling for aperture
Summary
Calcium influx to the cytosol (from the apoplast or from organellar stores) is central to elevation of cytosolic free Ca2+ ([Ca2+]cyt) as a second messenger in developmental, stress and immune signalling [1]. Members of the Glutamate Receptor-Like (GLR) family of ion channel sub-units mediate Ca2+ influx into pollen tubes and root cells [6,7]. In pollen tubes, they coreside with members of the Cyclic Nucleotide-Gated Channel (CNGC) family [8]. It is possible that annexins could be recruited directly to membranes, independently of vesicle delivery, to operate in stimulus-specific signalling. This short review will introduce this family of Ca2+-binding proteins and address what is known about their role in Ca2+ signalling in plants
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