Movement Protein of Tobacco Mosaic Virus Modifies Plasmodesmatal Size Exclusion Limit

TLDR

The 30‑kDa movement protein of tobacco mosaic virus facilitates cell‑to‑cell spread of viral progeny. A novel technique delivered non‑plasmalemma‑permeable fluorescent probes into the cytosol of tobacco mesophyll cells to assess plasmodesmatal size‑exclusion limits in transgenic plants expressing the MP gene. Transgenic plants expressing the MP allowed 9.4‑kDa F‑dextran to move between cells, whereas controls restricted movement to 700–800 Da, showing that the MP directly enlarges plasmodesmatal size‑exclusion limits without metabolizing the probe.

Abstract

The function of the 30-kilodalton movement protein (MP) of tobacco mosaic virus is to facilitate cell-to-cell movement of viral progeny in an infected plant. A novel method for delivering non-plasmalemma-permeable fluorescent probes to the cytosol of spongy mesophyll cells of tobacco leaves was used to study plasmodesmatal size exclusion limits in transgenic plants that express the MP gene. Movement of fluorescein isothiocyanate-labeled dextran (F-dextran) with an average molecular mass of 9400 daltons and an approximate Stokes radius of 2.4 nanometers was detected between cells of the transgenic plants, whereas the size exclusion limit for the control plants was 700 to 800 daltons. No evidence of F-dextran metabolism in the leaves of the transgenic plants was found. Thus, the tobacco mosaic virus movement protein has a direct effect on a plasmodesmatal function.