Truncation of a P1 leader proteinase facilitates potyvirus replication in a non‐permissive host

Summary The Potyviridae family is a major group of plant viruses that includes c. 200 species, most of which have narrow host ranges. The potyvirid P1 leader proteinase self‐cleaves from the remainder of the viral polyprotein and shows large sequence variability linked to host adaptation. P1 proteins can be classified as Type A or Type B on the basis, amongst other things, of their dependence or not on a host factor to develop their protease activity. In this work, we studied Type A proteases from the Potyviridae family, characterizing their host factor requirements. Our in vitro cleavage analyses of potyvirid P1 proteases showed that the N‐terminal domain is relevant for host factor interaction and suggested that the C‐terminal domain is also involved. In the absence of plant factors, the N‐terminal end of Plum pox virus P1 antagonizes protease self‐processing. We performed extended deletion mutagenesis analysis to define the N‐terminal antagonistic domain of P1. In viral infections, removal of the P1 protease antagonistic domain led to a gain‐of‐function phenotype, strongly increasing local infection in a non‐permissive host. Altogether, our results shed new insights into the adaptation and evolution of potyvirids.