Dynamics of the rice yellow mottle disease in western Burkina Faso: Epidemic monitoring, spatio-temporal variation of viral diversity, and pathogenicity in a disease hotspot.

The rice yellow mottle virus (RYMV) is a model in plant virus molecular epidemiology, with the reconstruction of historical introduction routes at the scale of the African continent. However, information on patterns of viral prevalence and viral diversity over multiple years at a local scale remains scarce, in spite of potential implications for crop protection. Here, we describe a 5-year (2015-9) monitoring of RYMV prevalence in six sites from western Burkina Faso (geographic areas of Bama, Banzon, and Karfiguela).

A Flexible and Original Architecture of Two Unrelated Zinc Fingers Underlies the Role of the Multitask P1 in RYMV Spread.

Viruses of the sobemovirus genus are plant viruses, most of which generate very important agricultural and financial losses. Among them, the rice yellow mottle virus (RYMV) is one of the most damaging pathogens devastating rice fields in Africa. RYMV infectivity and propagation rely on its protein P1, identified as a key movement and potential long-distance RNA silencing suppressor.

An atypical class of non-coding small RNAs is produced in rice leaves upon bacterial infection.

Non-coding small RNAs (sRNA) act as mediators of gene silencing and regulate plant growth, development and stress responses. Early insights into plant sRNAs established a role in antiviral defense and they are now extensively studied across plant-microbe interactions. Here, sRNA sequencing discovered a class of sRNA in rice (Oryza sativa) specifically associated with foliar diseases caused by Xanthomonas oryzae bacteria.

Complete genome sequence of a novel marafivirus infecting pearl millet in Burkina Faso.

Pearl millet (Pennisetum glaucum (L.) R. Br.

Optimized RNA-Silencing Strategies for Resistance in Rice.

(RRSV) is one of the most damaging viruses of the rice culture area in south and far-eastern Asia. To date, no genetic resistance has been identified and only expensive and non-environmentally friendly chemical treatments are deployed to fight this important disease. Non-chemical approaches based on RNA-silencing have been developed as resistance strategies against viruses.

Spatiotemporal Survey of Multiple Rice Diseases in Irrigated Areas Compared to Rainfed Lowlands in the Western Burkina Faso.

Multiple constraints affect rice yields in West Africa. Among these constraints are viral, bacterial, and fungal pathogens. We aimed to describe the spatiotemporal patterns of occurrence and incidence of multiple rice diseases in farmers' fields in contrasting rice growing systems in the western Burkina Faso.

Characterization of virus species associated with sweetpotato virus diseases in Burkina Faso.

Sweetpotato () production in sub-Saharan Africa is severely affected by viral diseases caused by several interacting viruses, including sweet potato feathery mottle virus (SPFMV), sweet potato chlorotic stunt virus (SPCSV), and sweet potato leaf curl virus (SPLCV). However, the aetiology of viral symptoms on sweetpotato is rarely established in most countries in Africa. Here, we aimed to investigate and characterize the incidence of sweetpotato viruses in Burkina Faso.

Design of a new multiplex PCR assay for rice pathogenic bacteria detection and its application to infer disease incidence and detect co-infection in rice fields in Burkina Faso.

Crop diseases are responsible for considerable yield losses worldwide and particularly in sub-Saharan Africa. To implement efficient disease control measures, detection of the pathogens and understanding pathogen spatio-temporal dynamics is crucial and requires the use of molecular detection tools, especially to distinguish different pathogens causing more or less similar symptoms. We report here the design a new molecular diagnostic tool able to simultaneously detect five bacterial taxa causing important diseases on rice in Africa: (1) Pseudomonas fuscovaginae, (2) Xanthomonas oryzae, (3) Burkholderia glumae and Burkholderia gladioli, (4) Sphingomonas and (5) Pantoea species.

Virus-based pharmaceutical production in plants: an opportunity to reduce health problems in Africa.

Background: Developing African countries face health problems that they struggle to solve. The major causes of this situation are high therapeutic and logistical costs. Plant-made therapeutics are easy to produce due to the lack of the safety considerations associated with traditional fermenter-based expression platforms, such as mammalian cells.

Nicotiana benthamiana is a suitable transient system for high-level expression of an active inhibitor of cotton boll weevil α-amylase.

Background: Insect resistance in crops represents a main challenge for agriculture. Transgenic approaches based on proteins displaying insect resistance properties are widely used as efficient breeding strategies. To extend the spectrum of targeted pathogens and overtake the development of resistance, molecular evolution strategies have been used on genes encoding these proteins to generate thousands of variants with new or improved functions.

Optimized transitory ectopic expression of promastigote surface antigen protein in Nicotiana benthamiana, a potential anti-leishmaniasis vaccine candidate.

In recent years, plants have been shown to be an efficient alternative expression system for high-value pharmaceuticals such as vaccines. However, constitutive expression of recombinant protein remains uncertain on their level of production and biological activity. To overcome these problems, transitory expression systems have been developed.

Virus-Bacteria Rice Co-Infection in Africa: Field Estimation, Reciprocal Effects, Molecular Mechanisms, and Evolutionary Implications.

Simultaneous infection of a single plant by various pathogen species is increasingly recognized as an important modulator of host resistance and a driver of pathogen evolution. Because plants in agro-ecosystems are the target of a multitude of pathogenic microbes, co-infection could be frequent, and consequently important to consider. This is particularly true for rapidly intensifying crops, such as rice in Africa.

OsMADS26 Negatively Regulates Resistance to Pathogens and Drought Tolerance in Rice.

Functional analyses of MADS-box transcription factors in plants have unraveled their role in major developmental programs (e.g. flowering and floral organ identity) as well as stress-related developmental processes, such as abscission, fruit ripening, and senescence.

P2 of Rice grassy stunt virus (RGSV) and p6 and p9 of Rice ragged stunt virus (RRSV) isolates from Vietnam exert suppressor activity on the RNA silencing pathway.

In Vietnam, the two main viruses that cause disease in rice are the Rice grassy stunt virus (RGSV) and the Rice ragged stunt virus (RRSV). Outbreaks of these two viruses have dramatically decreased rice production in Vietnam. Because natural resistance genes are unknown, an RNAi strategy may be an alternative method to develop resistance to RGSV and RRSV.

Sites under positive selection modulate the RNA silencing suppressor activity of rice yellow mottle virus movement protein P1.

RNA silencing is a eukaryotic mechanism for RNA-based gene regulation that plays an essential role in diverse biological processes, such as defence against viral infections. The P1 of rice yellow mottle virus (RYMV) is a movement protein and displays RNA silencing suppression activity with variable efficiency, depending on the origin of the isolates. In this study, the positive selection pressure acting on the P1 protein gene was assessed.

The RYMV-encoded viral suppressor of RNA silencing P1 is a zinc-binding protein with redox-dependent flexibility.

Viral suppressors of RNA interference (VSRs) target host gene silencing pathways, thereby operating important roles in the viral cycle and in host cells, in which they counteract host innate immune responses. However, the molecular mechanisms of VSRs are poorly understood. We provide here biochemical and biophysical features of the dual suppressor/activator VSR P1 protein encoded by the rice yellow mottle virus.

[Plant viruses RNA silencing suppressors: characterization and mechanism of action].

RNA silencing or Post-transcriptional gene silencing (PTGS) in plants is a fundamental defence mechanism against viruses, transgenes and transposons. Most viruses, if not all, are able to overcome RNA-silencing through the production of so-called "silencing suppressors" with counterdefence ability". This strategy is well known for plant and animal viruses.

The rice yellow mottle virus P1 protein exhibits dual functions to suppress and activate gene silencing.

In plants RNA silencing is a host defense mechanism against viral infection, in which double-strand RNA is processed into 21-24-nt short interfering RNA (siRNA). Silencing spreads from cell to cell and systemically through a sequence-specific signal to limit the propagation of the virus. To counteract this defense mechanism, viruses encode suppressors of silencing.

Identification of precursor transcripts for 6 novel miRNAs expands the diversity on the genomic organisation and expression of miRNA genes in rice.

Background: The plant miRNAs represent an important class of endogenous small RNAs that guide cleavage of an mRNA target or repress its translation to control development and adaptation to stresses. MiRNAs are nuclear-encoded genes transcribed by RNA polymerase II, producing a primary precursor that is subsequently processed by DCL1 an RNase III Dicer-like protein. In rice hundreds of miRNAs have been described or predicted, but little is known on their genes and precursors which are important criteria to distinguish them from siRNAs.

Biological and molecular characterization of a putative new sobemovirus infecting Imperata cylindrica and maize in Africa.

A new virus was isolated from both the grass Imperata cylindrica and maize plants that had yellow mottle symptoms in Burkina Faso, West Africa. The virus has isometric particles ca. 32 nm in diameter.

The Arabidopsis AtNPR1 inversely modulates defense responses against fungal, bacterial, or viral pathogens while conferring hypersensitivity to abiotic stresses in transgenic rice.

The nonexpressor of pathogenesis-related (PR) genes (NPR1) protein plays an important role in mediating defense responses activated by pathogens in Arabidopsis. In rice, a disease-resistance pathway similar to the Arabidopsis NPR1-mediated signaling pathway one has been described. Here, we show that constitutive expression of the Arabidopsis NPR1 (AtNPR1) gene in rice confers resistance against fungal and bacterial pathogens.

Genetic diversity and silencing suppression effects of Rice yellow mottle virus and the P1 protein.

Background: PTGS (post-transcriptional gene silencing) is used to counter pathogenic invasions, particularly viruses. In return, many plant viruses produce proteins which suppress silencing directed against their RNA. The diversity of silencing suppression at the species level in natural hosts is unknown.

Rice yellow mottle virus stress responsive genes from susceptible and tolerant rice genotypes.

Background: The effects of viral infection involve concomitant plant gene variations and cellular changes. A simple system is required to assess the complexity of host responses to viral infection. The genome of the Rice yellow mottle virus (RYMV) is a single-stranded RNA with a simple organisation.

Proteome analysis of plant-virus interactome: comprehensive data for virus multiplication inside their hosts.

Known host-parasite molecular interactions are widespread among parasite families, but these interactions have to be particularly large considering that viruses generally encode few proteins. Although some particular virus-host interactions are well described, no global study has yet shown multiple and simultaneous interactions in a host-parasite biological system. To prove that these multiple interactions occur in biological conditions, the complexes formed by a plant virus (rice yellow mottle virus) and the proteins of its natural host (rice) were extracted and purified from infected tissue sample.

Population proteomics: an emerging discipline to study metapopulation ecology.

Proteomics research has developed until recently in a relative isolation from other fast-moving disciplines such as ecology and evolution. This is unfortunate since applying proteomics to these disciplines has apparently the potential to open new perspectives. The huge majority of species indeed exhibit over their entire geographic range a metapopulation structure, occupying habitats that are fragmented and heterogeneous in space and/or through time.