Strawberry Vein Banding Virus P6 Protein Is a Translation Trans-Activator and Its Activity Can be Suppressed by FveIF3g

P25 and P37 proteins encoded by firespike leafroll-associated virus are viral suppressors of RNA silencing

Firespike leafroll-associated virus (FLRaV) is a major pathogen associated with firespike (Odontonema tubaeforme) leafroll disease. Phylogenetic analysis showed that FLRaV possesses typical traits of subgroup II members of ampeloviruses, but encodes two additional proteins, P25 and P37. Here, we determined the microfilament localization of P25 protein. Posttranscriptional gene silencing (PTGS) assay showed that both FLRaV P25 and P37 were able to suppress the local and systemic PTGS and FLRaV P25 was capable of suppressing the green fluorescent protein (GFP) gene silencing triggered by both sense RNA-induced PTGS (S-PTGS) and inverted repeat RNA-induced PTGS (IR-PTGS). In contrast, FLRaV P37 was only able to inhibit the GFP silencing triggered by the S-PTGS but not the IR-PTGS. In the transcriptional gene silencing (TGS) assay, only FLRaV P25 was found to be able to reverse established TGS-mediated silencing of GFP in 16-TGS plants. We also found that FLRaV P25 could aggravate the disease symptom and viral titer of potato virus X in N. benthamiana. These results suggest that FLRaV P25 and P37 may have crucial roles in overcoming host RNA silencing, which provides key insights into our understanding of the molecular mechanisms underlying FLRaV infection.

Strawberry Vein Banding Virus Movement Protein P1 Interacts With Light-Harvesting Complex II Type 1 Like of Fragaria vesca to Promote Viral Infection

Chlorophyll a/b-binding protein of light-harvesting complex II type 1 like (LHC II-1L) is an essential component of photosynthesis, which mainly maintains the stability of the electron transport chain. However, how the LHC II-1L protein of Fragaria vesca (FvLHC II-1L) affects viral infection remains unclear. In this study, we demonstrated that the movement protein P1 of strawberry vein banding virus (SVBV P1) interacted with FvLHC II-1L in vivo and in vitro by bimolecular fluorescence complementation and pull-down assays. SVBV P1 was co-localized with FvLHC II-1L at the edge of epidermal cells of Nicotiana benthamiana leaves, and FvLHC II-1L protein expression was upregulated in SVBV-infected F. vesca. We also found that FvLHC II-1L effectively promoted SVBV P1 to compensate for the intercellular movement of movement-deficient potato virus X (PVX^ΔP25) and the systemic movement of movement-deficient cucumber mosaic virus (CMV^ΔMP). Transient overexpression of FvLHC II-1L and inoculation of an infectious clone of SVBV showed that the course of SVBV infection in F. vesca was accelerated. Collectively, the results showed that SVBV P1 protein can interact with FvLHC II-1L protein, which in turn promotes F. vesca infection by SVBV.

Expression Analysis and Interaction Protein Screening of CRY1 in Strawberry

Cryptochrome 1 (CRY1), a main blue light receptor protein, plays a significant role in several biological processes. However, the expression patterns and function of CRY1 in strawberry have not been identified. Here, the expression profile of CRY1 in different tissues and developmental stages of strawberry fruit, and expression patterns response to abiotic stresses (low temperature, salt and drought) were analyzed. Its subcellular localization, interaction proteins and heterologous overexpression in tobacco were also investigated. The results showed that CRY1 was mainly expressed in leaves and fruits with an expression peak at the initial red stage in strawberry fruit. Abiotic stresses could significantly induce the expression of CRY1. The CRY1 protein was located in both nucleus and cytoplasm. Five proteins (CSN5a-like, JAZ5, eIF3G. NF-YC9, and NDUFB9) interacting with CRY1 were discovered. Genes related flowering times, such as HY5 and CO, in three overexpressed FaCRY1 tobacco lines, were significantly upregulated. Taken together, our results suggested CRY1 have a broad role in biological processes in strawberry.

Functional analysis of a viral promoter from a strawberry vein banding virus isolate from China

Background

Promoters are important factors affecting gene expression in cells. The driven activities of viral promoters were generally assessed to screen available promoters for transgenic and research and biotech industries. In this study, we cloned a full-length promoter from a Chinese isolate of strawberry vein banding virus (SVBV) and produced several deletion mutants for evaluation of applications in production of reporter proteins in stable transgenic plants.

Methods

The full-length promoter of SVBV (SP1) and its three deletion mutants (SP2, SP3, and SP4) were amplified using polymerase chain reaction. The effects of SVBV SP1, SP2, SP3, and SP4 on gene expression were evaluated using β-glucuronidase (GUS) and green fluorescent protein (GFP) reporter genes.

Results

Transient expression assays showed that the SVBV SP1 promoter and its three deletion mutants all expressed the reporter genes, albeit at very different levels. Interestingly, transcriptional activity driven by the SP1 promoter was much higher than that of the cauliflower mosaic virus (CaMV) 35S promoter. After stable transformation of the GUS gene into Nicotiana tabacum plants, SVBV SP1-driven transgene expression was approximately 2.6-fold higher than CaMV 35S promoter-driven transgene expression. In addition, GUS gene expression levels were enhanced by co-inoculation of the plants with the SP1 promoter-driven vector carrying the GUS gene and the vector expressing SVBV open reading frame (ORF) V or ORF VI.

Conclusions

The SVBV SP1 promoter from the Chinese isolate evaluated in this study could successfully drive transient and stable expression in plants, it was a stronger promoter than the CaMV 35S and FLt-US promoters and may be more useful for the production of stable transgenic plants.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12985-022-01778-2.

RNA-dependent RNA polymerase 1 delays the accumulation of viroids in infected plants

RNA-dependent RNA polymerase 1 (RDR1) is essential for plant antiviral defence, but its role in plant defence against viroid infection remains unknown. The present study aimed to identify the function and mechanism of RDR1 in plant resistance to viroid infection. Overexpression of Nicotiana tabacum RDR1 (NtRDR1) delayed the accumulation of potato spindle tuber viroid (PSTVd) genomic RNA and PSTVd-derived small RNA (sRNA) in Nicotiana benthamiana plants at the early invasion stage, but not in the late stage of infection. Conversely, virus-induced gene silencing of tomato RDR1 (SlRDR1a) increased the susceptibility to PSTVd infection (increased viroid accumulation). Salicylic acid (SA) pretreatment induced SlRDR1a expression and enhanced the defence against PSTVd infection in tomato plants. Our study demonstrated that RDR1 is involved in SA-mediated defence and restricts the early systemic invasion by PSTVd in plants. The decreased PSTVd accumulation in N. benthamiana was not caused by efficient accumulation of PSTVd sRNAs. These results deepen our understanding of the mechanism of RDR1 in plant defence responses to viroid attack.

The role of eukaryotic initiation factor 3 in plant translation regulation

Regulation of translation represents a critical step in the regulation of gene expression. In plants, the translation regulation plays an important role at all stages of development and, during stress responses, functions as a fast and flexible tool which not only modulates the global translation rate but also controls the production of specific proteins. Regulation of translation is mostly focused on the initiation phase. There, one of essential initiation factors is the large multisubunit protein complex of eukaryotic translation initiation factor 3 (eIF3). In all eukaryotes, the general eIF3 function is to scaffold the formation of the translation initiation complex and to enhance the accuracy of scanning mechanism for start codon selection. Over the past decades, additional eIF3 functions were described as necessary for development in various eukaryotic organisms, including plants. The importance of the eIF3 complex lies not only at the global level of initiation event, but also in the precise translation regulation of specific transcripts. This review gathers the available information on functions of the plant eIF3 complex.