Actin-Dependent Chloroplast Anchoring is Regulated by Ca2+-Calmodulin in Spinach Mesophyll Cells

• Published in: Plant and cell physiology 2011-11, Vol.52 (11), p.1973-1982
• Main Authors: Takamatsu, Hideyasu, Takagi, Shingo
• Format: Article
• Language: English
• ISSN: 0032-0781; 1471-9053
• DOI: 10.1093/pcp/pcr130

Chloroplasts are actively anchored at the appropriate intracellular regions to maintain advantageous distribution patterns under specific environmental conditions. Redistribution of chloroplasts is accompanied by their de-anchoring and re-anchoring, respectively, from and to the cortical cytoplasm. In spinach mesophyll cells, high-intensity blue light and Ca2+ treatment induced the disappearance of the meshwork-like array of actin filaments surrounding chloroplasts, which was suppressed by a calmodulin antagonist. Regulatory mechanisms of chloroplast anchoring were investigated using plasma membrane (PM) ghosts, on which the cortical cytoplasm underlying the PM was exposed. Addition of an actin-depolymerizing reagent or >1 µM Ca2+ induced detachment of a substantial number of chloroplasts from the PM ghosts concomitant with disordered actin organization. Calmodulin antagonists and anti-calmodulin antibodies negated the effects of Ca2+. In addition, Ca2+-induced detachment of chloroplasts was no longer evident on the calmodulin-depleted PM ghosts. We propose that chloroplasts are anchored onto the cortical cytoplasm through interaction with the actin cytoskeleton, and that Ca2+-calmodulin-sensitized de-anchoring of chloroplasts is a critical early step in chloroplast redistribution induced by environmental stimuli.