Laboratory of Virology, Wageningen University, Netherlands.
Abstracts of the papers presented at the International Conference of Indian Virological Society on “Emerging and Re-emerging viral Diseases of the Tropics and Subtropics” at Indian Agricultural Research Institute, New Delhi, India, December 11–14, 2007.
Tospoviruses represent the plant-infecting members of the large family of Bunyaviridae, which are characterized by having an enveloped particle and a tripartite RNA genome of which the segments can be negative-stranded or ambisense, depending on the genus. The genus Tospovirus currently encompasses 13 established species and another 8 tentative species, but with improving diagnostics and higher alertness probably considerable more species will be found. Tomato spotted wilt virus (TSWV) is the most widespread and most devastating tospovirus, which is efficienly transmitted by a.o. Thrips tabaci and Frankliniella occidentalis. Within the genome of TSWV a set of 5 genes encodes 6 mature proteins, i.e. the structural proteins N, G1 and G2, the L protein (viral RdRP), and 2 non-structural proteins NSm and NSs. Over the past years we have been studying the function of these two latter proteins and disclosed their functions as being the movement protein (MP) and the silencing (RNAi) suppressor protein (SSP), respectively. The NSm protein belongs to the class of tubule-forming MP's which facilitate cell-to-cell movement of viral nucleocapsids by tubules which assemble in plasmodesmata. While most plant viral SSP's perform their action by sequestering siRNAs the tospoviral NSs is also able to bind long dsRNA, thus being able to block both DICER action and siRNA loading of RISC complexes. In this aspect tospoviral NSs differs from NS3, the SSP of the closely related tenuiviruses, which only can bind siRNA. The capacity of tospoviral NSs (and tenuiviral NS3) to bind siRNAs enables these viruses to counteract antiviral RNAi in both their plant host and their insect vector. Besides experimental data also some evolutionary reflections will be presented.
