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

Plant viruses of the families Potyviridae and Secoviridae encode 3C-like proteases (3CL) that are related to picornavirus 3C proteases. This review discusses recent advances in deciphering the multifunctional activities of plant virus 3CL. 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. Future perspectives are discussed including using proteomic and degradomic techniques to elucidate the network of interactions of plant virus 3CL with the host proteome.