Mimicking carboxyterminal phosphorylation differentially effects subcellular distribution and cell-to-cell movement of Tobacco mosaic virus movement protein

Phosphorylation of Tobacco mosaic virus movement protein (TMV-MP) at three carboxyterminal Ser/Thr sites negatively regulates TMV-MP gating function and viral spread in Nicotiana tabacum but not in Nicotiana benthamiana, indicating a host dependant inactivation strategy. Here, we examine the effect of mimicking carboxyterminal phosphorylation on cell-to-cell transport of TMV-MP protein itself in host plants Nicotiana clevelandii, N. benthamiana, Nicotiana glutinosa and N. tabacum. Since TMV-MP transport function was inactivated only in N. tabacum, this host was chosen to explore the contribution of individual carboxyterminal phosphorylation sites. Selective mimicking of phosphorylation at one site enhances TMV-MP cell-to-cell transport, whereas a negative effect requires mimicking of phosphorylation at two or three sites. Potentially, during viral infection in N. tabacum, MP phosphorylation may occur sequentially: first, MP phosphorylation at a single site might ensure effective viral movement; only thereafter, further phosphorylation events may lead to inactivation of TMV-MP transport function.