An actomyosin-like cytoskeleton in the cyanobiont (Nosctoc sp.) of Peltigera canina Eva-María Diaz a , Christophe Ampe b , Maleen van Troys b , Miguel Vicente-Manzanares c , María-Estrella Legaz a , Carlos Vicente a, * a Team of Cellular Interactions in Plant Symbiosis, Faculty of Biology, Complutense University, Madrid, Spain b Department of Biochemistry, UGent, Gent, Belgium c Ramón & Cajal Program, Autonoma University, School of Medicine, Madrid, Spain A R T I C L E I N F O Article history: Received 10 March 2016 Accepted 6 May 2016 Available online xxx Keywords: Actin Cell motility Cytoskeleton Myosin Nostoc Peltigera canina A B S T R A C T Lichenized Nostoc cells isolated from the lichen Peltigera canina develop chemotaxis towards a lectin purified from the lichen thallus. Similar movements in unicellular eukaryotes require actin and myosin to generate contraction and relaxation along the chemotactic axis. We provide evidences for prokaryotic actin-like and myosin-like proteins in the cyanobiont Nostoc sp using cross-reacting antibodies against a- and b-actin and non-muscle myosin II light and heavy chains, and two-dimensional gel electrophoresis to determine the isoelectric point (IP) of the actin-like protein. Actin antibodies bound to a single reactive Nostoc polypeptide of an approximate molecular mass of 50 kD with IP values between 4 and 7 pH, similar to eukaryotic actin. The myosin light chain antibody reacted with a Nostoc protein with an apparent molecular weight of 20 kDa and another of 48 kDa. Immunoprecipitation of cell free extracts using anti- heavy chain myosin separately yielded only one signal corresponding to a protein of a molecular weight around 200 kDa. A bioinformatics analysis indicated that (cyano)bacterial actins are rare but do exist. Our results are consistent with the possible existence of protein homologues of actins and myosins in cyanobionts of P. canina, suggesting the existence of an actin-like apparatus that supports chemotactic swimming. ã 2016 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved. 1. Introduction Cyanobacteria are one of the oldest known groups present on Earth. They are characterized by their ability to fix nitrogen and photosynthetic oxygen. Cyanobacteria are also highly resistant to extremely environmental stresses (Guven and Howard, 2006). Cyanobacteria must be one of the first groups to have acquired directional motility between morphologically diverse groups of phototrophic prokaryotes (Hoiczyk, 2000). The mechanism of motility has been considered as primitive and simple; however, only limited progress has been made in understanding the process (Okamoto and Ohmori, 2002). During the last 40 years, many models have been proposed to explain the mechanism of bacterial motility, including surfactant effects, moving chains of adhesions, rotating mem- brane-embedded rotors, and, more recently, slime extrusion through nozzles (Wolgemuth et al., 2002; Mignot et al., 2007). However, clear-cut evidence for any of these models has been lacking. Several findings suggested that this motility involves distributed motors and focal adhesion complexes (Sliusarenko et al., 2007). This proposed motility mechanism has similarities to eukaryotic focal adhesion complexes, in which cell-surface ligands, that provide anchor points with the extracellular matrix, are connected to the actin–myosin network in the interior of the cell (Wozniak et al., 2004). Some filamentous cyanobacteria, such as Nostoc sp., produce specialized gliding filaments in cells known as hormogonia, which constitute a brief, dispersive stage of their life cycles. Hormogonia are the infectious agents in the establishment of cyanobacteria– Abbreviations: BSA, bovine serum albumin; CHAPS, 3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate; DTT, dithiothreitol; HEPES, 4-(2-hydro- xyethyl)piperazine-1-ethanesulfonic acid; IPG, immobilized pH gradient; PBS, phosphate buffered saline; SDS-PAGE, sodium dodecyl sulfate-polyacrylamide gel electrophoresis; TBS, Tris-buffered saline; Tris, tris(hydroxymethyl)aminomethane. * Corresponding author. E-mail address: cvicente@bio.ucm.es (C. Vicente). http://dx.doi.org/10.1016/j.phytol.2016.05.005 1874-3900/ã 2016 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved. Phytochemistry Letters 16 (2016) 249–256 Contents lists available at ScienceDirect Phytochemistry Letters journa l home page : www.e lsevier.com/loca te/phyt ol