Major determinant of pathogenesis that affects the hyperplastic response of the host to viral infection. Mediates the induction of cell division in permissive cells, mainly in phloem. May act as a suppressor of RNA-mediated gene silencing, also known as post-transcriptional gene silencing (PTGS), a mechanism of plant viral defense that limits the accumulation of viral RNAs. Interacts with Arabidopsis thaliana RCH2, ASK7/ASK-eta and ASK6/ASK-zeta. Localizes to the cell periphery. Expressed in vascular tissues, and especially in phloem cells. Phosphorylated by Arabidopsis thaliana ASK7/ASK-eta mainly on threonine and serine residues. Belongs to the geminiviridae protein AC4/C4 family.