The molecular features of begomovirus genomes have been thoroughly characterized, with the functions of most genes being well understood. Although an increasing number of begomoviruses have been annotated to contain an AC5/C5 ORF, little is known regarding its function during virus infection. Recently, the scientist in the Institute of Plant Protection has made a great progress in research on the function of the AC5 protein. the related research results have been published in New Phytologist.

It is generally accepted that begomoviruses in the family Geminiviridae encode four proteins (from AC1/C1 to AC4/C4) using the complementary-sense DNA as template. Although AC5/C5 coding sequences are increasingly annotated in databases for many begomoviruses, the evolutionary relationships and functions of this putative protein in viral infection are obscure. In this study, the scientists in IPP-CAAS demonstrated several important functions of the AC5 protein of a bipartite begomovirus, Mungbean yellow mosaic India virus (MYMIV). Comparison of wild-type and ac5 mutant MYMIV viruses demonstrated that AC5 had a critical role in infection. Furthermore, they confirmed that AC5 activity affected symptom phenotypes, and suppressed both PTGS and TGS. The results demonstrated that MYMIV AC5 was a pathogenicity determinant and a potent RNA silencing suppressor that employed novel mechanisms to suppress antiviral defenses, and suggested that the AC5 function may be conserved among many begomoviruses.