Rapeseed protein hydrolysates (RPH) were obtained by enzymatic hydrolysis of rapeseed protein using Alcalase 2.4 L FG. The degree of hydrolysis (DH) of RPH was about 25% using pH-stat method. The antioxidant activities of RPH were investigated by employing several in vitro assay, including the 1,1-diphenyl-2-picrylhydrazyl (DPPH)/superoxide/hydroxyl radical scavenging assays, and reducing power assay. RPH showed scavenging activity against free radicals such as DPPH, superoxide, and hydroxyl radicals. The radical scavenging effect was in a dose-dependent manner, and the EC 50 values for DPPH, superoxide, and hydroxyl radicals were found to be 0.71, 1.05, and 4.92 mg/mL, respectively. In addition, the RPH also exhibited notable reducing power, which was 0.51 at 2.00 mg/mL. The data obtained by in vitro systems obviously established the antioxidant potency of RPH. Combined with the results of the amino acid profiles, RPH were believed to have high nutritive value in addition to antioxidant activities.

Summary Sugarcane mosaic virus (SCMV) is a pathogen of worldwide importance that causes dwarf mosaic disease on maize (Zea mays). Until now, few maize genes/proteins have been shown to be involved in resistance to SCMV. In this study, we characterized the role of maize phenylalanine ammonia‐lyases (ZmPALs) in accumulation of the defence signal salicylic acid (SA) and in resistance to virus infection. SCMV infection significantly increased SA accumulation and expression of SA‐responsive pathogenesis‐related protein genes (PRs). Interestingly, exogenous SA treatment decreased SCMV accumulation and enhanced resistance. Both reverse transcription‐coupled quantitative PCR and RNA‐Seq data confirmed that expression levels of at least four ZmPAL genes were significantly up‐regulated upon SCMV infection. Knockdown of ZmPAL expression led to enhanced SCMV infection symptom severity and virus multiplication, and simultaneously resulted in decreased SA accumulation and PR gene expression. Intriguingly, application of exogenous SA to SCMV‐infected ZmPAL‐silenced maize plants decreased SCMV accumulation, showing that ZmPALs are required for SA‐mediated resistance to SCMV infection. In addition, lignin measurements and metabolomic analysis showed that ZmPALs are also involved in SCMV‐induced lignin accumulation and synthesis of other secondary metabolites via the phenylpropanoid pathway. In summary, our results indicate that ZmPALs are required for SA accumulation in maize and are involved in resistance to virus infection by limiting virus accumulation and moderating symptom severity.

Positive-stranded RNA viruses usually remodel host endomembrane system to form virus-induced intracellular vesicles for replication during infections. The genus Potyvirus of Potyviridae represents the largest number of positive single-stranded RNA viruses and causes great damage on crop production worldwide. Though potyviruses have wide host ranges, each potyvirus infects relatively limited host species. Phylogenesis and host range analysis can divide potyviruses into monocot-infecting and dicotinfecting groups, suggesting that some infection mechanism, probably on replication may be distinct for each group. Comprehensive studies on the model dicot-infecting turnip mosaic virus indicated that the 6K2-induced replication vesicles are derived from endoplasmic reticulum (ER) and subsequently target chloroplasts for viral genome replication. However, we have no knowledge on the replication site of monocot-infecting potyviruses. In this study, we rstly show that the precursor 6K2-VPg-Pro polyproteins of dicot-infecting potyviruses and monocot-infecting potyviruses phylogenetically cluster in two separate groups. With a typical gramineae-infecting potyvirus sugarcane mosaic virus (SCMV), we found that SCMV replicative double-stranded RNA (dsRNA) forms aggregates in cytoplasm but does not associate with chloroplasts. SCMV 6K2-VPg-Pro-induced vesicles colocalize with replicative dsRNA. Moreover, SCMV 6K2-VPg-Pro-induced structures target multiple intracellular organelles including ER, Golgi apparatus, mitochondria and peroxisomes, and have no evident association with chloroplasts. In conclusion, SCMV remodels multiple intracellular organelles for its genomic RNA replication.

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RNA silencing is an evolutionarily homology-based gene inactivation mechanism and plays critical roles in plant immune responses to acute or chronic virus infections, which often pose serious threats to agricultural productions. Plant antiviral immunity is triggered by virus-derived small interfering RNAs (vsiRNAs) and functions to suppress virus further replication via a sequence-specific degradation manner. Through plant-virus arms races, many viruses have evolved specific protein(s), known as viral suppressors of RNA silencing (VSRs), to combat plant antiviral responses. Numerous reports have shown that VSRs can efficiently curb plant antiviral defense response via interaction with specific component(s) involved in the plant RNA silencing machinery. Members in the family Closteroviridae (closterovirids) are also known to encode VSRs to ensure their infections in plants. In this review, we will focus on the plant antiviral RNA silencing strategies, and the most recent developments on the multifunctional VSRs encoded by closterovirids. Additionally, we will highlight the molecular characters of phylogenetically-associated closterovirids, the interactions of these viruses with their host plants and transmission vectors, and epidemiology.

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