A plastid protein crucial for Ca²⁺‐regulated stomatal responses

Abstract

Summary• Guard cell movements are regulated by environmental cues including, for example, elevations in extracellular Ca 2+ concentration. Here, the subcellular localization and physiological function of the Ca 2+ -sensing receptor (CAS) protein was investigated.• CAS protein localization was ascertained by microscopic analyses of green fluorescent protein (GFP) fusion proteins and biochemical fractionation assays. Comparative guard cell movement investigations were performed in wild-type and cas lossof-function mutant lines of Arabidopsis thaliana. Cytoplasmic Ca 2+ dynamics were addressed in plants expressing the yellow cameleon reporter protein YC3.6.• This study identified CAS as a chloroplast-localized protein that is crucial for proper stomatal regulation in response to elevations of external Ca 2+. CAS fulfils this role through modulation of the cytoplasmic Ca 2+ concentration.• This work reveals a novel role of the chloroplast in cellular Ca 2+ signal transduction.

Comparison of global responses to mild deficiency and excess copper levels in Arabidopsis seedlings

“…8,11,50 CAS is required for photoacclimation in Chlamydomonas reinhardtii, and particularly for proper stomatal regulation in response to raised external Ca 2+ . 51,52 These results suggest chloroplast to be a sensor of unbalanced Cu supply where signalling molecules, such as Ca 2+ , ROS and ABA, may participate in global plant responses to Cu status.…”

Calcium-dependent regulation of cyclic photosynthetic electron transfer by a CAS, ANR1, and PGRL1 complex

“…Ca 2+ -binding proteins are required for Ca 2+ sensing (9), and there is emerging evidence that chloroplasts may contribute to cellular Ca 2+ signaling via the chloroplast-localized Ca 2+ sensor protein CAS. CAS function is crucial for stomatal regulation (10,11) and chloroplast-mediated activation of immune signaling (12) in A. thaliana, as well as effective photo-acclimation in C. reinhardtii by controlling the expression of light harvesting complex stress-related protein 3 (LHCSR3) (13). This protein is crucial for qE, the energy-dependent component of nonphotochemical quenching (NPQ), which regulates thermal dissipation of excess absorbed light energy (14).…”

A Novel Calcium Binding Site in the Slow Vacuolar Cation Channel TPC1 Senses Luminal Calcium Levels

“…One could speculate that in Nt-TPC1b the combination of both mutant features resulted in the observed extremely long activation times. (Nomura et al, 2008;Weinl et al, 2008). Besides chloroplasts, vacuoles are postulated to represent important calcium stores.…”