Soil-Borne Wheat Mosaic Virus (SBWMV) 37 kDa Protein Rescues Cell-to-Cell and Long-Distance Movement of an Immobile Tobacco Mosaic Virus Mutant in Nicotiana benthamiana, a Non-Host of SBWMV

To verify the role and examine the functional range of the 37 kDa putative movement protein (MP) of soil-borne wheat mosaic virus (SBWMV), the 37 kDa gene was inserted into an infectious tobacco mosaic virus (TMV)-based expression vector (p30B), to generate p30BMP. The 30 kDa cell-to-cell MP gene of TMV was then inactivated (in p30BMP to give p30BDeltaMP) by a frameshift mutation which removed 80 amino acids from its C-terminus. Systemic infection of Nicotiana benthamiana plants occurred following inoculation with in vitro transcripts of p30BMP or p30BDeltaMP. Progeny viral RNAs from inoculated and systemically infected leaves were analysed by reverse transcriptase polymerase chain reaction and ApaI digestion, and by sequencing. The 30 kDa TMV MP or its truncated form were detected, respectively, in Western blots of cell wall protein extracts from p30BMP-transcript or p30BDeltaMP-transcript inoculated or systemically infected N. benthamiana leaves. High levels of SBWMV 37 kDa MP were detected in all cases. The results suggest that the 37 kDa protein of SBWMV, a monocotyledonous-infecting furovirus, can complement both cell-to-cell and long-distance movement functions in a defective heterologous virus (TMV) in N. benthamiana, a non-host of SBWMV.