J. Plant Biol. (2015) 58:75-86 DOI 10.1007/s12374-014-0541-z Players at Plasmodesmal Nano-channels Ritesh Kumar 1,† , Dhinesh Kumar 1,† , Tae Kyung Hyun 1,2,† and Jae-Yean Kim 1, * 1 Division of Applied Life Science (BK21plus/WCU program), Plant Molecular Biology & Biotechnology Research Center, Gyeongsang National University, Jinju 660-701, Korea 2 Department of Industrial Plant Science & Technology, College of Agricultural, Life and Environmental Sciences, Chungbuk National University, Cheongju 361-763, Korea Received: December 2, 2014 / Accepted: December 4, 2014 © Korean Society of Plant Biologists 2015 Abstract Plasmodesmata (PD) are the nano-channels connecting the adjacent plant cells. These functional tiny holes in the plant cell wall allow the symplasmic transport of diverse molecules such as RNA, proteins, phytohormones, metabolites and ions between the neighboring plant cells in order to conduct the both short distance and the long distance communications. Such PD-mediated symplasmic transport plays significant role in the various developmental and physiological processes in plants. To get deeper insight into the function and regulation of PD, in this review, we provide an overview on the various PD components at the cellular and the molecular level. The basic structure of PD reveals that these are membrane rich environments comprising plasma membrane (PM)-lined pores that make the continuity between the cell wall and central axial element of appressed endoplasmic reticulum (Desmotubule) in order to provide membrane and symplasmic connection between adjacent cells. Using diverse approaches, up to now more than 30 proteins including several transmembrane proteins and other non-protein components have been found to be PD associated. Next challenge will be to integrate known PD components to build complete structure of these functional nano-channels. Keywords: Callose, Cell-to-cell communication, Endoplasmic reticulum, Intercellular trafficking, Plasma membrane, Plasmodesmata Introduction Plasmodesmata (PD) are not new to this modern world of plant science, these were first recognized by Edaurd Tangl (1879) and he described PD as ‘open communications’ between protoplasts of endosperm cells in the cotyledons of Strychnos nuxvomica. Strasburger (1901) was the first to name these connections as ‘Plasmodesmata’. Although PD nanochannels were discovered more than a century ago, their precise structure, composition and function remain still elusive. PD are highly dynamic symplasmic channels which launch intercellular canals for the movement of nutrients and developmental messengers, which includes various hormones, proteins and RNA molecules (Cilia and Jackson 2004; Oparka 2004; Kim 2005; Ham et al. 2012; Han et al. 2014). Animal system is gifted by similar set up which allows symplasmic connection between adjacent cells known as ‘gap junctions’ (Elias and Kriegstein 2008). PD keeps on changing its structure and components in accordance to the need of plant system (Burch-Smith et al. 2011). According to classical terminology, PD is of two types, primary PD and secondary PD. Initially cytokinesis leads to formation of primary PD at the cell plate of division walls, which is simple pore structure. With the expansion of cell, secondary PD arises. They are classified further into two types; one which comes up from simple PD to form twinned PD and the one which arises from utterly de novo in cell walls without pre-existing PD. Ehler and van Bel (2010) emphasized on the model that PD formation progresses as the cell wall loosens and expands horizontally and which leads to insertion of new cell wall material in between PD. Another model suggested that PD may develop into branched structure with its central cavity being embedded in the cell wall (Oparka et al. 1999; Faulkner et al. 2008). Basically, PD is the junction between two cells which shares three main components of cell: plasma membrane (PM), cytoplasm and REVIEW ARTICLE † Authors contributed equally to this work. *Corresponding author; Jae-Yean Kim Tel : +82-55-772-1361 E-mail : kimjy@gnu.ac.kr