Family: Secoviridae

Genus: Sadwavirus

Distinguishing features

Members of the genus Sadwavirus have a bipartite genome, one or two capsid proteins (CPs), and some of them are transmitted by aphids; phylogenetic analysis places members of this genus as a distinct lineage of the family Secoviridae, close to the members of the sub-family Comovirinae. The genus Sadwavirus was recently reorganized to consist of three subgenera: Satsumavirus, Stramovirus and Cholivirus (Sanfaçon et al., 2020).

Virion

See discussion under family description. 

Genome organisation and replication

Similar to comoviruses, satsuma dwarf virus (subgenus Satsumavirus) has two CPs, one large and one small, but other members of the genus Sadwavirus (subgenera Stramovirus and Cholivirus) have a single CP (Iwanami 2008). The genome of sadwaviruses is bipartite and the genomic organization is similar to that of comoviruses, although a N-terminus coding domain seems to be lacking within the polyprotein encoded by RNA2. The proteinase of sadwaviruses is distinct from that of other viruses in the family in that it does not have a conserved His or Leu in the active site. In addition, the cleavage sites recognized by sadwavirus proteinases are unique with an A or a T at the −1 position (Table 3.Secoviridae). In contrast to comoviruses, there is no evidence that two overlapping polyproteins are encoded by RNA2. Similar to some nepoviruses, extensive sequence identity between RNA1 and RNA2 are found in the 5ʹ-UTRs, as well as in the 5ʹ-end of the putative coding region.

Biology

See discussion under family description. 

Species demarcation criteria

This is only a single species genus.