H2020 MelonMixVir Project: Mixed viral infections in melon: disease, vector transmission, RNA silencing suppression, and plant defense
- Type Project
- Status Filled
- Execution 2015 -2017
- Assigned Budget 170.121,6 €
- Scope Europeo
- Main source of financing H2020
- Project website MelonMixVir
The aim of the project was to understand the RNA silencing pathway in melon and explore ways to interfere with essential steps to reduce damage. To achieve these goals, we analyzed the RNA silencing pathway using susceptible melon plants infected with CYSDV and WMV. The virus's defense mechanism in plants involves inhibiting RNA silencing through the activity of proteins that block or reduce this defense mechanism. These viral proteins, RNA silencing suppressors (RSSs), play a key role during plant infection.
First, we developed a protocol to infect plants using the natural vectors of CYSDV and WMV, whitefly and aphid, respectively, and to obtain MVI. We then monitored infection symptoms by comparing single- and mixed-infected plants, and took samples every 12 days until 60 days of infection to compare virus levels. Our observations indicated that plants with MVI were more affected than those with SVI. However, after 60 days, plants with MVI showed recovery from disease symptoms compared to WMV-infected plants (see figure). Virus quantification revealed that CYSDV levels were always higher in mixed-infected plants. WMV, on the other hand, behaved in the opposite way (lower WMV in mixed-infected plants).
Next, we studied virus transmission to determine whether it is altered when insects acquire viruses from single- or mixed-infected plants. To this end, we allowed insects to acquire CYSDV and WMV from either SVI or MVI plants (whiteflies and aphids transmitting CYSDV and WMV) and transmit the virus to healthy melon seedlings (primary transmission). We also performed secondary transmission where recipient plants were pre-infected with a virus (aphids transmitted WMV to CYSDV-infected plants and vice versa) to see whether the presence of one virus inhibited the arrival of the second. In both primary and secondary transmission, there was no difference in the CYSDV transmission rate when whiteflies acquired CYSDV from single- or mixed-infected plants. However, to our surprise, in the case of WMV transmission, we observed a higher transmission rate when aphids acquired CYSDV from mixed-infected plants. This result was unexpected, as virus quantification showed that the amount of WMV decreases in plants with MVI compared to plants with SVI. That is, there is a lower amount of WMV in plants with MVI, but the virus transmission rate is higher when this is the source plant. Members of the group are currently conducting complementary experiments to further elucidate these results.
Finally, we investigated whether there was any interaction or relationship between the RSS of both viruses during MVI. First, we confirmed the RSS activity of the proteins described for each virus and then performed subcellular localization experiments that suggested colocalization of some of these proteins within the plant cell.
To fulfill the most important objective of scientific research, the results obtained were disseminated to both the scientific community and the general public. They were presented at five scientific meetings (national and international) and regularly at the host institute's internal seminars. For the general public, various initiatives were undertaken to bring science closer to society, and six outreach activities were carried out.
Like all living beings, plants are subject to attack by various pathogens (bacteria, fungi, and viruses) that cause enormous losses in global agriculture.
Viruses constitute one of the most damaging biotic stresses affecting crops. In nature, single viral infections (SVIs) usually cause mild or no symptoms, facilitating their spread through the dispersal of asymptomatic infected plants. In contrast, in mixed viral infections (MVIs), probably the most common, the plant is simultaneously infected with two or more viruses. This can lead to synergistic effects, with the resulting disease presenting more intense symptoms than with SVIs. Effective control of these viral diseases requires epidemiological information on their spread (around 80% of all plant viruses are transmitted by insect vectors). Furthermore, MVIs can modify virus dissemination parameters by altering virus-vector-host interactions.
In some cases, the importance of MVI is well known, for example, in sweet potato viral disease (SVD), but in many others, the limited knowledge available makes it difficult to assess the risk they pose. Cucurbits such as melon are a good example of this situation: despite the frequent incidence of mixed viral infections (MVI) (as demonstrated by recent field studies), only a few comprehensive studies have been initiated in this crop to date.
A deeper understanding of the mechanisms involved in IVMs would help minimize their negative effects on various crops worldwide, increasing productivity and avoiding losses, which would translate into direct economic benefits for society.
MelonMixVir addressed the phytosanitary challenge posed by IVM in a critically important crop in Europe: melon. The main objective was to provide science-based advice to minimize IVM damage in melon, with the aim of improving production and quality of this crop and, consequently, economic benefits for Europe. We proposed a systematic analysis of pathosystems combining hosts, viruses, and vectors to explore the effects of their interactions.
The overall objectives of MelonMixVir were: 1) Pathology of mixed infections: to determine the severity and extent of a mixed infection in melon and to identify proactive measures to control the virus and potential solutions to minimize its damage; 2) Entomology and vector transmission: to analyze virus transmission by insect vectors (aphids/whiteflies) during IVM in order to provide practical advice and approaches to control virus dissemination; 3) Molecular biology and resistance: to determine the role of the viral defense system acting during IVM in melon that could modulate the resistance response of host plants.
We conclude that, in the case of IMV in melon plants caused by WMV (Watermelon mosaic virus) and CYSDV (Cucurbit dwarf virus), a synergy likely exists, with WMV benefiting from the presence of CYSDV (at least in transmission). The relative abundance of each virus is altered by the presence of the other, indicating that they somehow interact within the plant.
MelonMixVir addresses mixed viral infections in melon plants. Pathogenic viruses are collectively responsible for significant economic losses worldwide, but most plant virology studies are conducted with a few individual viruses, while frequent cases of mixed infections are clearly underrepresented. Conversely, severe synergistic effects can occur in mixed infections, even between viruses that cause mild or no symptoms when present alone. Consequently, the lack of knowledge about multiple infections hampers risk assessment in numerous crops. For example, in cucurbits, only a few studies address this situation, despite recent surveys showing the frequent occurrence of mixed infections. The main objective of MelonMixVir is to fill this gap by providing new knowledge and scientific advice to minimize virus damage in melon, thereby improving production and quality, and increasing economic benefits for Europe. To this end, we aim to explore potential similarities between melon plants coinfected by potyvirus (WMV) and crinivirus (CYSDV) with the better-known, similar pathosystem that results in sweet potato virus disease (SPVD). The comparative analysis will focus on several steps, including transmission by insect vectors (aphids and whiteflies), plant defense mechanisms (based on RNA silencing), and pathogen responses (via the action of RNA silencing suppressors). Approaches from virology, entomology, and molecular biology will be used to better understand the different processes. This ambitious project is designed to complement the candidate's expertise, allowing her to progress into a career as a plant pathologist. Outcomes include the design of new management strategies and recommendations to reduce virus damage. The work will be conducted in close collaboration with a partner organization, the private seed company Semillas Fitó, to achieve a clear practical application of the knowledge generated.
To our knowledge, this is the first study to address MVI in melon in a systematic and controlled manner. We hope these results will help decipher MVI not only in melon, but also in other crops. The tools developed to manage the insect population will undoubtedly be very useful for future work addressing similar problems. Furthermore, transmission results can be of great value for controlling the spread of the virus in the field (such as controlling the whitefly population to minimize the presence of CYSDV and, consequently, the presence of mixed infected plants).
The results obtained here are the basis for producing melon plants with improved virus-resistant traits. This will have a direct, positive impact on the European economy by improving the sector's competitiveness and will benefit society by enabling the production, and consequently consumption, of higher-quality fruit. Furthermore, the potential uses and commercial value of the tools generated can be extended to other crops, broadening the impact of MelonMixVir's results beyond the limits of a single crop and a single geographic area.
- CENTRE DE RECERCA EN AGRIGENOMICA CSIC-IRTA-UAB-UB (CRAG-CERCA)
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