Abstract
Tobacco mosaic virus (TMV) is a positive-sense single-stranded RNA virus. The 3′ end of TMV genome is consisted of an upstream pseudoknot domain (UPD) and a tRNA-like structure (TLS), both of which are important RNA elements to enhance TMV replication and translation. Deep-sequencing analysis revealed that TMV-specific viral small interfering RNAs (vsiRNAs) were generated in TMV-infected Nicotiana benthamiana plants. A vsiRNA derived from the juxtaposition between UPD and TLS, named TMV-vsiRNA 22 nt (6285–6306), possessed high sequence complementarity to a host gene which encodes a C2-domain abscisic acid (ABA)-related (CAR) 7-like protein. CAR proteins play a critical role in ABA signaling pathway. The CAR protein-encoding gene was amplified from N. benthamiana leaves and termed as Nb-CAR7. In TMV-infected plants, accumulation of Nb-CAR7 transcripts was significantly decreased, as compared with that of mock-inoculated and TMV-43A-infected plants. TMV-43A is a mutant without the UPD sequence in its genome. Overexpression of Nb-CAR7 led to decreased TMV RNA accumulation in the TMV-inoculated leaves. Silencing of Nb-CAR7 enhanced TMV replication and resulted in a higher viral RNA accumulation. In addition, the expression level of Nb-CAR7 was positively correlated to that of a low-temperature-induced ABA responsive gene (LTI65). The effect of Nb-CAR7 on TMV RNA accumulation in host plants was linked to ABA signaling pathway. In conclusion, a vsiRNA derived from the juxtaposition between UPD and TLS at the 3′UTR of TMV targets a host CAR7 gene.
Highlights
Tobacco mosaic virus (TMV) is a positive-sense singlestranded Ribonucleic acid (RNA) virus in genus Tobamovirus
Results Viral small interfering RNA (vsiRNA) derived from the upstream pseudoknot domain (UPD) region of TMV genome was detected in TMV-infected N. benthamiana plants Based on our previously published results on small RNA sequencing of TMV-infected N. benthamiana plants, a total of 32,369 short interfering RNAs (siRNAs) reads were mapped to TMV genome (Guo and Wong 2017)
The vsiRNA generated from nucleotides 6285 to 6306 in TMV positive-sense strand showed the highest read counts and was termed as TMV-vsiRNA 22 nt (6285–6306) (Fig. 1a)
Summary
Tobacco mosaic virus (TMV) is a positive-sense singlestranded RNA virus in genus Tobamovirus. It has a wide host range and its infection can cause severe damages and yield losses in many economically important crops (Scholthof et al 2011). In its natural host tobacco and other closely related species, TMV can induce chlorosis, mosaic and necrosis in plant tissues. The upstream pseudoknot domain (UPD) and tRNA-like structure (TLS) in the 3′ UTR play important roles in virus replication (Gallie and Walbot 1990; Takamatsu et al 1990). The TLS of TMV can be aminoacylated and some primary RNA elements in UPD interact with host plant elongation factors during virus replication
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