Imaging plasmodesmata: studying the connections between plant cells across scales

Plasmodesmata (PD) are conduits between plant cells that are essential to multicellularity: they allow a wide range of molecules, such as nutrients, phytohormones, RNAs and proteins including transcription factors, to be transported from cell to cell. PD are essential to intercellular communication and have been shown to be important for developmental transitions. PD were discovered using light microscopy. Since then, advanced imaging approaches have been utilised to resolve PD ultrastructure, analyse their spatial distribution, and probe the translocation of diverse cargo. In this review, we first summarise the microscopy techniques used for studying PD, with a focus on fluorescence and electron microscopy (EM). We then discuss emerging techniques and new advances, such as Correlative Light and Electron Microscopy (CLEM), single-molecule imaging, and cryo-electron tomography (cryo-ET), approaches that will likely lead to exciting discoveries in the field, such as capturing dynamics at PD and revealing previously unknown aspects of PD structure. This review discusses the strengths and weaknesses of the different techniques and how combining them could pave the way to a more detailed understanding of the diverse PD types, their distribution and function.