Molecular and bioinformatics characterization of host and temperature dependent accumulation of dimeric viral RNA molecules derived from the S segment of Polygonun ringspot tospovirus
P. MARGARIA (1), A. Bertran (2), M. Ciuffo (3), C. Rosa (1), R. Oliveira Resende (2), M. Turina (3) (1) Pennsylvania State University, U.S.A.; (2) University of Brasília, Brazil; (3) Institute for Sustainable Plant Protection, Italy

Polygonum ringspot virus is a recently characterized tospovirus, originally isolated from Polygonum convolvulus in Italy. We have characterized new viral RNA species with nearly twice the size of the genomic S RNA, that accumulate specifically in some Nicotiana spp., and are particularly abundant in Nicotiana benthamiana (NB). These RNAs are linear, head-to-tail imperfect (containing deletions) dimers (IDs). ID-RNAs are present in total RNA preparations from purified nucleocapsids, but not in purified virions. RNAseq and RT-PCR analysis allowed us to characterize different dimer sequences in different PolRSV isolates.  Their biogenesis occurs in late stages of systemic infection in NB, and is temperature dependent. Interestingly, isolate Plg13/2 abundantly accumulated the IDs while having visually undetectable amounts of genomic S RNA, maintained IDs even at 18 C, and was not able to infect tomato, possibly suggesting that the dimer forms may interfere with viral infection and host range. IDs presence correlated with the abundant host-specific accumulation of viral sRNAs observed in infected NB, suggesting that the dimer forms are targets for silencing. We propose that the defective NB RNAi pathway, lacking the amplification phase, might be involved in IDs generation and persistence in the viral population. IDs were not detected in the thrips vector, but were common to an isolate of Tomato spotted wilt virus, indicating that dimer formation may be a general feature for tospoviruses. This is the first demonstration of S RNA dimers for Tospovirus, and of their occurrence at the organismal level in Bunyaviridae.

Abstract Number: P13-413
Session Type: Poster