A plastid protein crucial for Ca2+-regulated stomatal responses

Abstract

• Guard cell movements are regulated by environmental cues including, for example, elevations in extracellular Ca2+ 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 loss-of-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 Ca2+. CAS fulfils this role through modulation of the cytoplasmic Ca2+ concentration. • This work reveals a novel role of the chloroplast in cellular Ca2+ signal transduction. © The Authors (2008).