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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; 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.