P1-independent replication and local movement of Rice yellow mottle virus in host and non-host plant species

Wheat Yellow Mosaic Virus P1 Inhibits ROS Accumulation to Facilitate Viral Infection

Reactive oxygen species (ROS), as signaling molecules, play a crucial role in the plant immune response. However, the mechanism(s) by which viruses affect ROS metabolism remain largely unexplored. Here, we found that wheat yellow mosaic virus (WYMV)-encoded P1 is a pathogenic protein. Transcriptomic and proteomic integrative analyses were performed on WYMV-infected overexpressing-P1 wheat and wild-type plants. A total of 9245 differentially expressed genes (DEGs) and 1383 differentially expressed proteins (DEPs) were identified in the transcriptome and proteome, respectively. At their intersection, 373 DEGs/Ps were identified. Enrichment analysis revealed that the expression of genes related to the ROS metabolism pathway in overexpressed P1 transgenic wheat (OE-P1) plants significantly increased during WYMV infection. We screened peroxidase (TaPOD) and thioredoxin reductase (TaTrxR) as they showed the most significant differences in expression. The silencing of TaPOD and TaTrxR revealed that they positively regulate WYMV infection by reducing ROS accumulation. Furthermore, hydrogen peroxide treatment induced WYMV resistance in wild-type wheat plants and OE-P1 transgenic plants. This study provides a theoretical basis for the role of P1 in plant viral infection.

Rice Yellow Mottle Virus (RYMV): A Review

Rice (Oryza spp.) is mostly grown directly from seed and sown on wet or dry seed beds or usually used as transplants on nursery beds. Among all the economically important viral diseases in the world, rice yellow mottle virus (RYMV) is only prevalent in rice-growing countries in Africa. RYMV has become the main rice production constraint in Africa over the last 20-25 years, causing yield losses of 10 to 100% depending on the age of the plant at the time of infection, degree of varietal susceptibility and the existing climatic conditions. Good agricultural practices and biotechnological tools in the development of improved resistant cultivars have been extensively utilized in controlling the disease. This review focuses on RYMV, its epidemiology, serological and molecular typing, disease management and the way forward for sustainable rice production.

Rice yellow mottle virus is a suitable amplicon vector for an efficient production of an anti-leishmianiasis vaccine in Nicotiana benthamiana leaves

BACKGROUND

Since the 2000's, plants have been used as bioreactors for the transient production of molecules of interest such as vaccines. To improve protein yield, "amplicon" vectors based on plant viruses are used. These viral constructs, engineered to carry the gene of interest replicate strongly once introduced into the plant cell, allowing significant accumulation of the protein. Here, we evaluated the suitability of the monocot-infecting RNA virus Rice yellow mottle virus (RYMV) as an amplicon vector. The promastigote surface antigen (PSA) of the protozoan Leishmania was considered as a protein of interest due to its vaccine properties against canine leishmaniasis.

RESULTS

Since P1 (ORF1) and CP (ORF3) proteins are not strictly necessary for viral replication, ORF1 was deleted and the PSA gene was substituted to ORF3 in the RYMV-based vector. We evaluated its expression in the best described plant bioreactor system, Nicotiana benthamiana which, unlike rice, allows transient transformation by Agrobacterium. Despite not being its natural host, we demonstrated a low level of RYMV-based vector replication in N. benthamiana leaves. Under optimized ratio, we showed that the P19 silencing suppressor in combination with the missing viral CP ORF significantly enhanced RYMV amplicon replication in N. benthamiana. Under these optimized CP/P19 conditions, we showed that the RYMV amplicon replicated autonomously in the infiltrated N. benthamiana cells, but was unable to move out of the infiltrated zones. Finally, we showed that when the RYMV amplicon was expressed under the optimized conditions we set up, it allowed enhanced PSA protein accumulation in N. benthamiana compared to the PSA coding sequence driven by the 35S promoter without amplicon background.

CONCLUSION

This work demonstrates that a non-dicot-infecting virus can be used as an amplicon vector for the efficient production of proteins of interest such as PSA in N. benthamiana leaves.

Citrate-Citric Acid RNA Isolation (CiAR) for Fast, Low-Cost, and Reliable RNA Extraction from Multiple Plant Species and Tissues

RNA isolation is routinely carried out in many laboratories for different downstream applications. Although protocols for this can vary between labs depending on the specific plant species and tissues under study and the preferences of their researchers, these protocols usually include the use of volatile organic and toxic chemicals. As an alternative, several companies offer less hazardous RNA extraction kits, but these kits significantly increase the cost per sample and are thus not affordable for every lab, especially when a large number of samples is to be processed. We have previously described a fast and efficient method for RNA isolation from plant vegetative tissues that requires only two home-made, simple, inexpensive, and nontoxic buffers. Both buffers have low concentrations of citric acid and its sodium salt. The first buffer also contains a detergent to help with nucleic acid solubilization while keeping RNases inactive. The second buffer has sodium chloride at high molarity to separate protein from nucleic acids. RNA is precipitated, and contaminating DNA can then be optionally removed. Here, we describe and expand on this approach, which we call the citrate-citric acid RNA isolation, or CiAR, method. We provide a detailed description of the protocol, describe a modification to make it compatible with non-vegetative tissues, and compile and extend the number of species and tissues to which it can be applied. © 2021 Wiley Periodicals LLC.

Insights Into Natural Genetic Resistance to Rice Yellow Mottle Virus and Implications on Breeding for Durable Resistance

Rice is the main food crop for people in low- and lower-middle-income countries in Asia and sub-Saharan Africa (SSA). Since 1982, there has been a significant increase in the demand for rice in SSA, and its growing importance is reflected in the national strategic food security plans of several countries in the region. However, several abiotic and biotic factors undermine efforts to meet this demand. Rice yellow mottle virus (RYMV) caused by Solemoviridae is a major biotic factor affecting rice production and continues to be an important pathogen in SSA. To date, six pathogenic strains have been reported. RYMV infects rice plants through wounds and rice feeding vectors. Once inside the plant cells, viral genome-linked protein is required to bind to the rice translation initiation factor [eIF(iso)4G1] for a compatible interaction. The development of resistant cultivars that can interrupt this interaction is the most effective method to manage this disease. Three resistance genes are recognized to limit RYMV virulence in rice, some of which have nonsynonymous single mutations or short deletions in the core domain of eIF(iso)4G1 that impair viral host interaction. However, deployment of these resistance genes using conventional methods has proved slow and tedious. Molecular approaches are expected to be an alternative to facilitate gene introgression and/or pyramiding and rapid deployment of these resistance genes into elite cultivars. In this review, we summarize the knowledge on molecular genetics of RYMV-rice interaction, with emphasis on host plant resistance. In addition, we provide strategies for sustainable utilization of the novel resistant sources. This knowledge is expected to guide breeding programs in the development and deployment of RYMV resistant rice varieties.