Phototropins Function in High-Intensity Blue Light-Induced Hypocotyl Phototropism in Arabidopsis by Altering Cytosolic Calcium

• Published in: Plant physiology (Bethesda) Vol. 162; no. 3; pp. 1539 - 1551
• Main Authors: Zhao, Xiang, Wang, Yan-Liang, Qiao, Xin-Rong, Wang, Jin, Wang, Lin-Dan, Xu, Chang-Shui, Zhang, Xiao
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Biologists 01-07-2013
• Subjects: Arabidopsis - metabolism; Arabidopsis - physiology; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Auxins; Biological and medical sciences; Calcium; Calcium - metabolism; Calmodulin - genetics; Calmodulin - metabolism; Cell membranes; Curvature; Cytosol - metabolism; Fluence; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Plant; Hypocotyl - physiology; Hypocotyls; Indoleacetic Acids - metabolism; Intracellular Signaling Peptides and Proteins - genetics; Intracellular Signaling Peptides and Proteins - metabolism; Light; Membrane Proteins; Membrane Transport Proteins - genetics; Membrane Transport Proteins - metabolism; Movements; Mutation; Phosphoproteins - genetics; Phosphoproteins - metabolism; Phototropism; Phototropism - physiology; Plant cells; Plant physiology and development; Plants, Genetically Modified; Protein Serine-Threonine Kinases; Receptors; Seedlings; Signal Transduction; SIGNALING AND RESPONSE; Arabidopsis thaliana; Hypocotyl; Calcium; Plant physiology; Cruciferae; Dicotyledones; Angiospermae; Phototropism; Spermatophyta; Blue light; Experimental plant; Cytosol
• ISSN: 0032-0889; 1532-2548; 1532-2548
• DOI: 10.1104/pp.113.216556

Phototropins (phot1 and phot2), the blue light receptors in plants, regulate hypocotyl phototropism in a fluence-dependent manner. Especially under high fluence rates of blue light (HBL), the redundant function mediated by both photl and phot2 drastically restricts the understanding of the roles of phot2. Here, systematic analysis of phototropin-related mutants and overexpression transgenic lines revealed that HBL specifically induced a transient increase in cytosolic Ca concentration ([Ca²⁺]
cyt
) in Arabidopsis (Arabidopsis thaliana) hypocotyls and that the increase in [Ca²⁺]
cyt
was primarily attributed to phot2. Pharmacological and genetic experiments illustrated that HBL-induced Ca²⁺ increases were modulated differently by phot1 and phot2. Phot2 mediated the HBL-induced increase in [Ca²⁺]
cyt
mainly by an inner store-dependent Ca²⁺-release pathway, not by activating plasma membrane Ca²⁺ channels. Further analysis showed that the increase in [Ca²⁺]
cyt
was possibly responsible for HBL-induced hypocotyl phototropism. An inhibitor of auxin efflux carrier exhibited significant inhibitions of both phototropism and increases in [Ca²⁺]
cyt
, which indicates that polar auxin transport is possibly involved in HBL-induced responses. Moreover, PHYTOCHROME KINASE SUBSTRATE1 (PKS1), the phototropin-related signaling element identified, interacted physically with phototropins, auxin efflux carrier PINFORMED1 and calcium-binding protein CALMODULIN4, in vitro and in vivo, respectively, and HBL-induced phototropism was impaired in pks multiple mutants, indicating the role of the PKS family in HBL-induced phototropism. Together, these results provide new insights into the functions of phototropins and highlight a potential integration point through which Ca²⁺ signalingrelated HBL modulates hypocotyl phototropic responses.