C4A and infection: For example, BSCTV infection or expression of BSCTV C4 protein in A. thaliana caused leaf malformation, upregulated the expression of several cell cycle-related genes: cycloidea (CYC), cyclin-dependent kinase (CDK) and proliferating cell nuclear antigen (PCNA), and downregulated the expression of CDK inhibitor and retinoblastoma-related gene (RBR1) (Park et al., 2010).