The C5 protein encoded by Ageratum leaf curl Sichuan virus is a virulence factor and contributes to the virus infection.

Earlier reports have indicated that begomoviruses encode four proteins (AC1/C1, AC2/C2, AC3/C3, and AC4/C4 proteins) using complementary-sense DNA as the template. In recent years, several reports have shown that some begomoviruses also encode an AC5/C5 protein from the complementary DNA strand, and these AC5/C5 proteins play different roles in virus infections. Here, we provide evidence showing that Ageratum leaf curl Sichuan virus (ALCScV), a monopartite begomovirus, also encodes a C5 protein that is important for disease symptom formation and can affect viral replication. Infection of Nicotiana benthamiana plants with a potato virus X (PVX)-based vector carrying the ALCScV C5 gene resulted in more severe disease symptoms and higher virus accumulation levels. ALCScV C5 protein can be found in the cytoplasm and the nucleus. Furthermore, this protein is also a suppressor of posttranscriptional gene silencing. Mutational analysis showed that knockout of C5 gene expression significantly reduced ALCScV-induced disease symptoms and virus accumulation, while expression of the C5 gene using the PVX-based vector enhanced ALCScV accumulation in coinfected N. benthamiana plants.

Identification of a novel pepper-infecting monopartite begomovirus in China.

Three full-length monopartite begomovirus sequences were obtained from two field-collected pepper plants exhibiting severe leaf yellowing disease symptoms in Yunnan province of China. The three full-length viral sequences contain 2,748 nucleotides (nt) and share the highest nt sequence similarity (88.2% identity) with that of malvastrum yellow vein Yunnan virus (MYVYNV). The betasatellite molecules of the two viruses share the highest sequence similarity (99.3% identity) with that of malvastrum yellow vein Yunnan betasatellite (MYVYNB). Based on the current species demarcation criteria for the genus Begomovirus, these three newly identified isolates can be considered members of a novel monopartite Begomovirus species, and we have named this virus "pepper yellow leaf curl virus" (PepYLCV). Phylogenetic analysis showed that PepYLCV clustered with pepper leaf curl Yunnan virus (PepLCYNV). Recombination analysis revealed that PepYLCV is likely to have originated through a recombination event between MYVYNV and tomato leaf curl Yunnan virus (TLCYnV).