The C4/AC4 proteins have diverse functions and are implicated in many different aspects of viral infection and pathogenicity; 1) transgenic expression of the curtovirus C4 gene induced hyperplasia in, and altered the development of, Nicotiana benthamiana [8] and Arabidopsis plants [9,10,11], 2) the C4 proteins of some curtoviruses and monopartite begomoviruses have been implicated in virus movement [11,12,13,14], and 3) the C4 proteins of some begomoviruses act as suppressors of gene silencing [15,16]. This evidence concerns the gene C4A and viral infectious disease.