Analyses of Ca2+ accumulation and dynamics in the endoplasmic reticulum of Arabidopsis root cells using a genetically encoded Cameleon sensor

Bonza M.C., Loro G., Behera S., Wong A., Kudla J., Costa A.

Abstract

In planta, very limited information is available about how the endoplasmic reticulum (ER) contributes to cellular Ca2+ dynamics and homeostasis. Here, we report the generation of an ER-targeted Cameleon reporter protein suitable for analysis of Ca2+ accumulation and dynamics in the lumen of the ER in plant cells. Using stably transformed Arabidopsis (Arabidopsis thaliana) plants expressing this reporter protein, we observed a transiently enhanced accumulation of Ca2+ in the ER in response to stimuli inducing cytosolic Ca2+ rises in root tip cells. In all experimental conditions, ER Ca2+ dynamics were substantially different from those monitored in the cytosol. A pharmacological approach enabled us to evaluate the contribution of the different ER-resident Ca2+-ATPase classes in the regulation of the ER Ca2+ homeostasis. Taken together, our results do not provide evidence for a role of the ER as a major source that releases Ca2+ for stimulus-induced increases in cytosolic Ca2+ concentration. Instead, our results show that the luminal ER Ca2+ elevations typically follow cytosolic ones, but with distinct dynamics. These findings suggest fundamental differences for the function of the ER in cellular Ca2+ homeostasis in plants and animals. © 2013 American Society of Plant Biologists. All Rights Reserved.