A model system for analyzing intercellular communication through plasmodesmata using moss protonemata and leaves.

Plant growth, development, and environmental responses require the proper regulation of intercellular movement of signals and nutrients. For this, plants have specialized cytoplasmic channels, the plasmodesmata (PD), which allow the symplasmic movement of micro- and macromolecules between neighboring cells. Internal and external signals spatio-temporally regulate the movement of molecules through the PD to control plant development and environmental responses. Although some aspects of targeted movement of molecules have been revealed, the mechanisms of non-targeted, diffusible flow of molecules through PD, and its regulation and function, remain poorly understood, particularly at the cellular level. Previously, we developed a system to quantitatively analyze non-targeted movement of a photoconvertible fluorescent protein, Dendra2, at the single-cell level in the filamentous protonemata tissue of the moss Physcomitrella patens. In protonemata, one-dimensional intercellular communication can be easily observed and quantitatively analyzed at the cellular level. In this review, we describe how protonemata and leaves of P. patens can be used to study symplasmic movement through PD, and discuss how this system can help improve our understanding of PD regulation and function in development and environmental responses in plants.