Papain-Like Cysteine Proteases Contribute to Functional Cleavage of Begomoviral V2 Effector Required for Relevant Virulences.

The begomoviral V2 protein is known to be multifunctional, including its interaction with and inhibition of CYP1, a papain-like cysteine protease (PLCP). However, the effect of this interaction on viral pathogenicity remains unclear. Cotton leaf curl Multan virus (CLCuMuV), a typical monopartite begomovirus associated with a betasatellite, is one of the main pathogens responsible for cotton leaf curl disease. This study verifies the interaction between CLCuMuV V2 and NbCP15, a PLCP homologue in Nicotiana benthamiana. The results show that V2 can be cleaved by NbCP15 in vitro, with the N-terminal cleavage site located between the second and third amino acids. Using an Agrobacterium-mediated inoculation method, we investigated the influence of cleavage sites on viral pathogenicity. The findings indicate that mutation of the third amino acid in V2 (V2^D3A) reduced the pathogenicity of both heterologous PVX and CLCuMuV. Additionally, the NbCP15 gene mutation in N. benthamiana (nbcp15) also resulted in reduced CLCuMuV pathogenicity. These results suggest that CLCuMuV V2 may promote viral infection through its interaction with plant PLCPs.