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Chrysanthemum virus B encodes a multifunctional p12 protein that acts as a transcriptional activator in the nucleus and as a suppressor of RNA silencing in the cytoplasm. Here, we investigated the impact of p12 on accumulation of major classes of small RNAs (sRNAs). The results show dramatic changes in the sRNA profiles characterised by an overall reduction in sRNA accumulation, changes in the pattern of size distribution of canonical siRNAs and in the ratio between sense and antisense strands, lower abundance of siRNAs with a U residue at the 5′-terminus, and changes in the expression of certain miRNAs, most of which were downregulated. Electronic supplementary material The online version of this article (10.1007/s00705-020-04832-y) contains supplementary material, which is available to authorized users.

Potato is the fourth most important crop worldwide that is used as a staple food, after rice, wheat and maize. The crop can be affected by a large number of pathogens, including fungi, oomycetes, bacteria and viruses. Diseases caused by viruses are among the most important factors contributing to reduced quality and yield of the crop. Potato mop-top virus (genus Pomovirus) induces necrotic flecks in the tuber flesh and skin of potato in temperate countries. Spongospora subterranea is the vector of PMTV. Both the virus and its vector cause disease in potato. In Colombia, PMTV has been detected throughout the country together with a novel pomo-like virus in the centre (Cundinamarca and Boyacá) and south west (Nariño) of the country. We studied the molecular and biological characteristics of this novel virus. Its genome resembles those of members of the genus Pomovirus, and it is closely related to PMTV. It induces mild systemic symptoms in Nicotiana benthamiana (mosaic, branch curling), but no symptoms in N. tabacum, N. debneyi and Chenopodium amaranticolor. The proposed name for the virus is "Colombian potato soil-borne virus" (CPSbV). Additionally, another pomo-like virus was identified in Nariño. This virus induces severe systemic stem declining and mild mosaic in N. benthamiana. The tentative name "soil-borne virus 2" (SbV2) is proposed for this virus. No vectors have been identified for these viruses despite several attempts. This work focused on the characterisation of CPSbV. The risk posed by these viruses if they are introduced into new territories is discussed.