Abstract
Potyviruses represent the largest group of known plant RNA viruses and include many agriculturally important viruses, such as Plum pox virus, Soybean mosaic virus, Turnip mosaic virus, and Potato virus Y. Potyviruses adopt polyprotein processing as their genome expression strategy. Among the 11 known viral proteins, the nuclear inclusion protein b (NIb) is the RNA-dependent RNA polymerase responsible for viral genome replication. Beyond its principal role as an RNA replicase, NIb has been shown to play key roles in diverse virus–host interactions. NIb recruits several host proteins into the viral replication complexes (VRCs), which are essential for the formation of functional VRCs for virus multiplication, and interacts with the sumoylation pathway proteins to suppress NPR1-mediated immunity response. On the other hand, NIb serves as a target of selective autophagy as well as an elicitor of effector-triggered immunity, resulting in attenuated virus infection. These contrasting roles of NIb provide an excellent example of the complex co-evolutionary arms race between plant hosts and potyviruses. This review highlights the current knowledge about the multifunctional roles of NIb in potyvirus infection, and discusses future research directions.
Highlights
Potyviridae is the largest family of known plant RNA viruses and is comprised of 10 definitive and 3 proposed genera [1,2]
We showed that Beclin1, a core component of autophagy, interacts with Turnip mosaic virus (TuMV) nuclear inclusion b (NIb), and targets NIb to autophagosomes for degradation [97]
These findings suggest a functional role of NIb as a pathogenesis determinant at least in some potyvirus–host combinations
Summary
Potyviridae is the largest family of known plant RNA viruses and is comprised of 10 definitive and 3 proposed genera [1,2]. Example species in Potyvirus include Potato virus Y (PVY), Plum pox virus (PPV), Soybean mosaic virus (SMV), Turnip mosaic virus (TuMV), Lettuce mosaic virus (LMV), Sweet potato feathery mottle virus (SPFMV), and Sugarcane mosaic virus (SCMV), 4 of which have been ranked in the 10 most economically or scientifically important plant viruses [4,5]. NIb functions in trans and may need other viral-replication-associated proteins and/or host factors to deliver its RdRp activity in the VRC [19]. Mature proteins resulting from polyprotein processing are indicated open reading frame (ORF) is indicated as a long box. Other cleavages are processed by NIaPro. The mature proteins include coat protein (CP), nuclear inclusion b (NIb), which is the viral RNA-dependent RNA polymerase (RdRp), and two viral suppressors of RNA silencing (VSRs), HC-Pro and VPg. For clarity, the relative sizes of the mature proteins are not drawn to scale.
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