The NIa-Protease Protein Encoded by the Pepper Mottle Virus Is a Pathogenicity Determinant and Releases DNA Methylation of Nicotiana benthamiana.

Yi-Nuo Gong,Jing Peng,Zhan-Hong Zhang,Yong Liu,Hui Liu,Xiang-Wen Luo,Song-Bai Zhang,De-Yong Zhang,Ru-Qing Tang,Ouyang Xian,Yu Zhang

doi:10.3389/fmicb.2020.00102

Abstract

It is well documented that the canonical function of NIa-protease (NIa-Pro) of the potyviruses is responsible for cleaving the viral polyprotein into functional proteins. Although NIa-Pro is vital for the infection cycle of potyviruses, the function of NIa-Pro in the interaction of the potyvirus host is not clear. In this study, NIa-Pro is ectopically expressed from a potato virus X (PVX) vector and infiltrates Nicotiana benthamiana wild type and 16-TGS. The pathogenicity and inhibition of host transcriptional gene silencing (TGS) are characterized. Ectopic expression of NIa-Pro from a PVX vector resulted in severe mosaic symptoms followed by a hypersensitive-like response in N. benthamiana. Furthermore, PepMoV NIa-Pro was able to reverse established TGS of a green fluorescent protein transgene by reducing methylation of promoter sequences in N. benthamiana and possessed the capacity to interfere with the global methylation of N. benthamiana. Taken together, the results of this study likely suggest that PepMoV NIa-Pro is a pathogenicity determinant and a potent suppressor of host TGS and suggest that NIa-Pro may employ novel mechanisms to suppress host antiviral defenses. To the best of our knowledge, this is the first report of a plant RNA virus modulating host TGS in a novel manner by interfering with the establishment of the methylation step of the plant DNA methylation pathway.

Highlights

Potyviruses constitute the largest group of plant-infecting RNA viruses affecting major crops worldwide
The functions of PepMoV-encoded NIa-Pro were characterized by ectopic expression of NIa-Pro from a potato virus X (PVX) vector, and the results demonstrated that PepMoV NIa-Pro is a pathogenicity determinant and a potent suppressor of host transcriptional gene silencing (TGS) and suggest that NIa-Pro may employ novel mechanisms to suppress host antiviral defenses
Sequence alignment showed that potyvirus NIa-Pro proteins are highly divergent in amino acid sequences

Summary

Introduction

Potyviruses (genus Potyvirus, family Potyviridae) constitute the largest group of plant-infecting RNA viruses affecting major crops worldwide. The main viral proteinase, NIa, is a polyprotein consisting of two domains, viral protein genome-linked (VPg) and protease (NIa-Pro), separated by an inefficiently utilized self-proteolytic site. NIa-Pro encoded by potyviruses plays many roles during the virus infecting cycle. The canonical function of NIa-Pro is the main protease of the virus responsible for the cleavage of most sites in the polyprotein (Sun et al, 2010). Tobacco etch potyvirus encoding NIa-Pro can bind NIb, which is critical for tobacco etch virus (TEV) genome replication (Daros et al, 1999). NIa-Pro induced vein necrosis in tobacco by potato virus Y (PVY) isolates (Faurez et al, 2012), which indicated that NIa-Pro of the potyviruses may be a pathogenicity determinant

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