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Tospovirus is the only member of the Bunyavirus family which infects plants (the other members infecting animals and humans). Tomato spotted wilt virus (TSWV), the most famous tospovirus, is a major pathogen for tomato and pepper cultures. Because there is no chemical treatment against viruses, the only way to fight them is to develop genetic resistance. Genetic resistances to tospoviruses are available, but are largely overcome. Therefore, there is an urgent need to characterize new sources of resistance. The aim of my PhD is to find new genetic resistances based on susceptibility factors, which are proteins required by the virus to accomplish its cycle and infect the plant. As a first step, I will develop a 3D model of the TSWV RNA-dependent RNA polymerase (RdRp), a key viral protein for its infectious cycle. Based on this model, a part of the RdRp protein will be selected as bait in order to identify plant protein interactors by yeast-two hybrid screening. Finally, I will search for new tomato alleles encoding variant forms of those tomato susceptibility factors. If those variants impair the interaction between the plant factor and the viral protein, those alleles are very likely to be associated with the crop resistance to the pathogen.

Developing genetic resistance is an important alternative to the use of pesticides in order to avoid viral infections in crops. However, this approach can be limited by the lack of natural resistant alleles available for plant breeding. Biotechnologies can supply for this lack by altering susceptibility host factors used by viruses. However, strategies relying on knocking out plant host factors can be undermined by associated developmental default, or gene redundancy (Gauffier et al., 2016). Synthetic biology could offer the opportunity to develop functional synthetic alleles associated with plant resistance at no developmental cost. The translation initiation factors (eIF4E), that are associated with resistance to most single strand positive RNA (including the major group of potyviruses), are the ideal targets to validate such approaches. We focused on the Arabidopsis thaliana eIF4E1 gene that encodes a susceptibility factor to a potyvirus, the Clover yellow vein virus. Artificial resistance alleles were created by directed mutagenesis and used to complement loss-of-function eif4e1 plants for assessing in planta both their functionality and resistance efficiency. By combining these synthetic resistance alleles with others eIF4E factors-mediated resistance, a broad resistance spectrum to potyviruses is expected as well as increased resistance durability. This study will make proof of the feasibility of this approach to obtaining large resistance spectrum in plants with the perspective of extending it to crops.

National audience

National audience; Tomato (Solanum lycopersicum) is one of the most cultivated vegetable in the world, but suffers from important yield losses caused by viral diseases. Therefore, the development and use of cultivars that are genetically resistant to viruses has become a critical factor of competitiveness for both breeders and producers and one of the key stakes for sustainable agriculture. In this context, generating new resistance alleles using biotechnological approaches (e.g., TILLING) appears as a powerful tool to diversify host targets to promote resistance against viruses.

National audience; Root-knot nematodes, Meloidogyne spp., are extremely polyphagous plant parasites worldwide. Since the use of most chemical nematicides is being prohibited, genetic resistance is an efficient alternative way ta protect crops against these pests. However, resistance genes (R-genes) are limited and nematode populations are able ta overcome them with time. Good management of these valuable resources is thus a key point of R-gene durability. ln pepper, Me3 is a dominant major resistance gene, currently used in breeding programs, that control M. arenario, M. incognito and M. javanica, the three main root-knot nematodes species. ln this study, it was introgressed in either a susceptible or a partially resistant genetic background in either homozygous or heterozygous allelic status. Confronting these genotypes with a high inoculation pressure of an avirulent M. incognito isolate or a Me3 virulent laboratory-selected population (obtained by successive re-inoculation on a Me3 R-pepper line) demonstrated i) that the genetic background plays an important raie, Me3 being overcome more easily in a susceptible genetic background than in a partially resistant one, ii) that the allelic status has no effect. These results are in good agreement with concepts recently developed from the analysis of very different plant-pathogen interactions: pepper-virus (Palloix et al., 2009) or rapeseed-Leptosphaeria (Brun et al., 2012). Experiments are now underway ta detect and localise genes or loci providing partial resistance (QTLs = Quantitative Trait Loci) ta root-knot nematodes explaining the differences observed between susceptible and partially resistant genetic backgrounds, and ta determine the effectiveness of their « protective » raie on the major R-genes. Ali these results are of main importance for the creation of new varieties by breeders who have to take into account the plant material used and the resistance gene they want ta introgress.