Geminiviruses are circular ssDNA containing plant viruses with a genome size of ~ 2.7 kb . Geminiviruses have an atypical genomic content. They are either monopartite with a single genomic component , monopartite with a satellite DNA that is around half the size of the genome  or bipartite with two genomic components of ~2.7 kb encoding different genes on both components . Monopartite viruses encode all the genes required for successful infection, replication and movement on the single genome. In case of monopartite viruses with satellite DNA and bipartite viruses, the DNA A contains the genes necessary for replication while the cognate genome component encodes genes for infectivity and movement within the plants [3, 5].
Whiteflies and leaf-hoppers are the vectors that transmit geminiviruses from one plant to other. These viruses replicate their DNA via rolling circle replication mechanism by utilizing the host plant cellular machinery [5–7]. Geminiviral proteins expressed after a successful viral infection in a plant cell induce the expression of host cell replication machinery from the differentiated plant cells [8–11]. The induced replication machinery is then diverted on to the viral DNA through the protein-protein interactions by the viral proteins for the productive replication [12–17].
Geminiviral proteins are often multi-functional in nature. Complementary strand of the geminiviruses encode four ORFs, viz., AC1, AC2, AC3 and AC4. Replication initiator protein (Rep/AC1/C1) is an essential viral protein for replication . It binds the viral DNA in a sequence specific manner by recognizing the iterons at the origin of replication on the viral DNA [19–22]. Rep functions as a site-specific endonuclease by recognizing the hairpin loop structure and sequence at the viral origin of replication to initiate the viral replication. It also functions as a ligase to terminate the replication of viral DNA [23–27]. Rep has the unique ability to act as a repressor of its own transcription [28, 29] and thereby regulates the expression of down-stream AC2 and AC3 genes . Rep is also an ATPase [26, 31, 32] and a helicase [32, 33]. In addition, it interacts with various host proteins [9, 13–16, 34, 35] and viral proteins [36, 37]. Similarly, the C2/AC2 protein of geminiviruses can bind to the DNA  and control the coat protein gene expression [39, 40] either by activation or derepression . AC2 is also known for its ability to suppress post-transcriptional gene-silencing mechanism [42–44] inside the host plant by inhibiting adenosine kinase [45, 46] or by reducing genome wide cytosine methylation . AC2 also inhibits SNF1 kinase to reduce the basal defense . Likewise, AC4/C4 protein from geminiviruses was also shown to have multiple functions with roles in post-transcriptional gene-silencing [49, 50], movement of virus inside the host cells [51, 52], cell division , transcription  and interacts with host protein AtSKeta - a protein from brassinosteroid signaling pathway .
Such a battery of multiple functions in viral proteins is most of the time brought out by their ability to form hetero-oligomer or homo-oligomer. In case of the geminiviral proteins, Rep/AC1 is able to bind, nick and ligate DNA as a monomer. However, its helicase activity is strictly dependent on its ability to form a higher order homo-oligomer [32, 33]. One possible way by which Rep is able to induce the replication machinery is through formation of a hetero-oligomer by interacting with retinoblastoma protein [9, 56]. Similarly, AC2 protein is capable of interacting with ADK and suppresses local gene-silencing as a monomer whereas it can transactivate the virion sense strand genes as an oligomer only . These observations indicate that the ability to form oligomers and to interact with other host proteins confers unique properties to the viral proteins which they cannot perform as monomers.
AC3 protein was shown to interact with viral protein AC1 [36, 58]. It was also shown to interact with host proteins like pRBR , PCNA  and SlNAC1 . AC3 was shown to enhance viral DNA replication by an unknown mechanism [60–65]. Preliminary studies on AC3 oligomerization suggested that AC3 also forms a higher order oligomer like AC1 [58, 66]. Together, these hetero and homo-oligomerization studies observed in case of AC3 suggest that it might also have multiple functions in addition to its role in replication which is unexplored as yet. In this study we tried to address the roles of Tomato leaf curl Kerala virus-[India:Kerala II:2005] (DQ85263) AC3 protein in the viral life cycle. We have performed an exhaustive phage display analysis to find out the interacting peptides of AC3 protein. These interacting peptides were observed to be homologous to proteins from various metabolisms indicating the likely role of AC3 in these cellular pathways. Since replication of viral DNA and gene-silencing are the two important phenomena that determine the progress of viral infection, we have chosen to investigate the role of AC3 in these biological processes. We have designed vectors to analyze the role of AC3 in replication and virus induced gene-silencing in both yeast and plants.