When NCAPP1 (blue) is blocked (bottom), its cargo (orange) does not pass through plasmodesmata.


In plants, cell-to-cell communication is achieved through plasmodesmata, unique intercellular organelles that establish cytoplasmic and ER continuity between neighboring cells. Jung-Youn Lee, William Lucas (University of California, Davis, CA), and colleagues now identify a selective gatekeeper for this system, which they call NCAPP1.

Plasmodesmata are the conduits for many non–cell-autonomous proteins (NCAPs). Lee et al. figured that some NCAPs might bind to plasmodesmal proteins, so they used an affinity column based on an NCAP called CmPP16 and a cell wall fraction highly enriched for plasmodesmal proteins to identify NCAPP1.

As expected for a plasmodesmal function, colocalization of NCAPP1 and CmPP16 was observed at the ER near the orifice to plasmodesmata. A dominant–negative form of NCAPP1 altered trafficking of the NCAPs CmPP16, LEAFY, and the movement protein of Tobacco mosaic virus, but left trafficking of other NCAPs unaffected. Thus, NCAP movement is a regulated process, similar to nuclear pore trafficking. Lucas' group is now purifying other potential plasmodesmal proteins that traffic NCAPP1-independent cargos. ▪


Lee, J.-Y., et al.