THRUMIN1 Is a Light-Regulated Actin-Bundling Protein Involved in Chloroplast Motility

• Published in: Current biology Vol. 21; no. 1; pp. 59 - 64
• Main Authors: Whippo, Craig W., Khurana, Parul, Davis, Phillip A., DeBlasio, Stacy L., DeSloover, Daniel, Staiger, Christopher J., Hangarter, Roger P.
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 11-01-2011
• Subjects: absorption; actin; Actins - metabolism; Arabidopsis - cytology; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; blue light; chloroplasts; Chloroplasts - physiology; Chloroplasts - radiation effects; Cytoskeleton - metabolism; Cytoskeleton - radiation effects; Gene Expression Regulation, Plant; Light; mammals; Microfilament Proteins - genetics; Microfilament Proteins - metabolism; microfilaments; photoreceptors; Plant Leaves - cytology; plasma membrane
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2010.11.059

Chloroplast movement in response to changing light conditions optimizes photosynthetic light absorption [1]. This repositioning is stimulated by blue light perceived via the phototropin photoreceptors [2–4] and is transduced to the actin cytoskeleton [5]. Some actin-based motility systems use filament reorganizations rather than myosin-based translocations [6]. Recent research favors the hypothesis that chloroplast movement is driven by actin reorganization at the plasma membrane [7, 8], but no proteins affecting chloroplast movements have been shown to associate with both the plasma membrane and actin filaments in vivo. Here we identified THRUMIN1 as a critical link between phototropin photoreceptor activity at the plasma membrane and actin-dependent chloroplast movements. THRUMIN1 bundles filamentous actin in vitro, and it localizes to the plasma membrane and displays light- and phototropin-dependent localization to microfilaments in vivo. These results suggest that phototropin-induced actin bundling via THRUMIN1 is important for chloroplast movement. A mammalian homolog of THRUMIN1, GRXCR1, has been implicated in auditory responses and hair cell stereocilla development as a regulator of actin architecture [9, 10]. Studies of THRUMIN1 will help elucidate the function of this family of eukaryotic proteins.
► THRUMIN1 is required for light-mediated chloroplast movement ► THRUMIN1 is anchored to the plasma membrane via residues predicted to be acylated ► THRUMIN1 localization to actin is regulated by the phototropin photoreceptors ► THRUMIN1 binds to and bundles actin filaments in vitro