The nucleocapsid and the non structural small proteins of Tomato spotted wilt virus (TSWV) strain Br01 are not sufficient for eliciting lethal necrosis in Nicotiana benthamiana and local necrotic lesions on Nicotiana tabacum
Ciuffo M, Pacifico D, Turina M
Istituto di Virologia Vegetale, CNR, Torino 10135, Italy.
Correspondence: m.ciuffo@ivv.cnr.it
We detected a consistent different phenotype on Nicotiana benthamiana and N. tabacum between the Br01 isolate and the Italian isolate p272. Based on the phenotype of a reassortant strain carrying the S genomic segment of p272, and the M and L genomic segments from strain Br01, we concluded that the small segment of Br01 is necessary for eliciting lethal necrosis on N. benthamiana and local necrotic lesions on N. tabacum. The aim of this work was to evaluate if the nucleocapsid and non-structural small proteins encoded by the small genomic segment of strain Br01 were able to cause the distinctive symptoms, alone or in combination. The two allelic variants (the Br01 and p272) of each protein were transiently expressed in planta through agroinfiltration. Symptoms were monitored in order to detect reaction specific to the Br01 alleles. As a positive control for a viral protein causing lethal necrosis and necrotic local lesion, we infiltrated p19 of Tomato bushy stunt virus (TBSV); as negative control, the protein green fluorescent protein was inserted in the pBin61 vector. Accumulation of nucleocapsid and non-structural small proteins were monitored through western blot analysis. Green fluorescent protein accumulation was monitored visually under UV light observation. All the different alleles of the nucleocapsid and NSs proteins readily accumulated in the infiltrated N. benthamiana and N. tabacum leaves; no necrotic reaction was observed in any of the single or combined agro-infiltration. A necrotic response was observed when p19 protein was infiltrated in both N. benthamiana and N. tabacum. Our results suggest that non-structural small proteins Br01 and N Br01 cannot cause a necrotic response alone or in combination. Our hypothesis involves the requirement of different regions of the M and L segmentsof the genome.
