3C-like proteases at the interface of plant-virus-vector interactions: Focus on potyvirid NIa proteases and secovirid...

Plant viruses of the families Potyviridae and Secoviridae encode 3C-like proteases (3CL^pro) that are related to picornavirus 3C proteases. This review discusses recent advances in deciphering the multifunctional activities of plant virus 3CL^pro. These proteases regulate viral polyprotein processing and facilitate virus replication. They are also determinants of host range, virulence, symptomatology and super-infection exclusion in some plant-virus interactions and facilitate aphid transmission. Potyvirid NIa-Pro proteases interact with host factors to interfere with a variety of defense mechanisms: salicylic acid-dependent signaling, ethylene-dependent signaling, transcriptional gene silencing and RNA decay. Potyvirid NIa-Pro also cleave host proteins at signature cleavage sites, although the biological impact of these cleavage remains to be determined. Recently, a plant defense mechanism was uncovered that inhibits the proteolytic activity of a comovirus 3CL^pro. Future perspectives are discussed including using proteomic and degradomic techniques to elucidate the network of interactions of plant virus 3CL^pro with the host proteome.