Abstract
Simple SummaryPolerovirus P0 proteins are multifunctional proteins. Besides their viral suppressor of RNA silencing (VSR) functions, several P0 proteins can induce a cell death phenotype within the infiltrated region of Nicotiana benthamiana or Nicotiana glutinosa. Recently, the Brassica yellows virus (BrYV) genotype A P0 protein (P0BrA) was identified as a strong viral suppressor of RNAi. In this study, we compared the features of the P0 proteins encoded by different genotypes of BrYV and revealed their difference in inducing cell death in N. benthamiana. Key residues in P0BrA for inducing cell death were also identified. We also showed that all three BrYV genotypes had synergistic interaction with PEMV 2 in N. benthamiana. This study provides theoretical guidance for controlling the viral disease caused by poleroviruses in the future.Brassica yellows virus (BrYV) is a tentative species of the genus Polerovirus, which has at least three genotypes (A, B, and C) in China. The P0 protein of BrYV-A (P0BrA) has been identified as a viral suppressor of RNA silencing (VSR), which can also induce cell death in infiltrated Nicotiana benthamiana leaves. In this study, we demonstrated that the cell death induced by P0BrA was accompanied by the accumulation of reactive oxygen species (ROS) and increased Pathogenesis-related protein genes-1 (PR1) expression. Meanwhile, this cell death phenotype was delayed by salicylic acid (SA) pretreatment. Biological function comparison of the three P0 proteins showed that transiently expressed P0BrB or P0BrC induced a significantly delayed and milder cell death response compared with P0BrA. However, like P0BrA, they also suppressed local and systemic RNA silencing. Six residues of P0BrA essential for inducing cell death were identified by comparative analysis and amino acid substitution assay. We also show that all three BrYV genotypes have synergistic interactions with pea enation mosaic virus 2 (PEMV 2) in N. benthamiana. This study provides theoretical guidance for controlling the viral disease caused by poleroviruses in the future.
Highlights
IntroductionThe P0 proteins have been identified as viral suppressor of RNA silencing (VSR) in many poleroviruses, including Turnip yellows virus (TuYV), Cucurbit aphid-borne yellows virus (CABYV), Potato leafroll virus (PLRV), Beet mild yellowing virus (BMYV), Cotton leafroll dwarf virus (CLRDV), Sugarcane yellow leaf virus (ScYLV), Melon aphid-borne yellows virus (MABYV), Maize yellow mosaic virus (MaYMV), Cereal yellow dwarf virus (CYDV), Wheat yellow dwarf virus-GPV isolate (WYDV-GPV), Maize yellow dwarf virusRMV 2 (MYDV-RMV2), and Pea mild chlorosis virus (PMCV) [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21]
DAB staining detected the accumulation of reactive oxygen species (ROS), a physiological response associated with the onset of hypersensitive responses (HR), in the infiltration regions of N. benthamiana leaves expressing the P0BrA protein (Figure 1A)
We demonstrated that the cell death induced by P0BrA was accompanied by the accumulation of ROS and induction of protein genes-1 (PR1) gene expression
Summary
The P0 proteins have been identified as VSR in many poleroviruses, including Turnip yellows virus (TuYV), Cucurbit aphid-borne yellows virus (CABYV), Potato leafroll virus (PLRV), Beet mild yellowing virus (BMYV), Cotton leafroll dwarf virus (CLRDV), Sugarcane yellow leaf virus (ScYLV), Melon aphid-borne yellows virus (MABYV), Maize yellow mosaic virus (MaYMV), Cereal yellow dwarf virus (CYDV), Wheat yellow dwarf virus-GPV isolate (WYDV-GPV), Maize yellow dwarf virusRMV 2 (MYDV-RMV2), and Pea mild chlorosis virus (PMCV) [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21]. The amino acid sequence of P0 proteins throughout the genus shows low identity and the RNA silencing suppressor (RSS) activity of the P0 proteins varies between different viruses. PLRV and PMCV P0 proteins contain a conserved F-box-like domain and suppress RNA silencing, they fail to interact with
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