Abstract :

Aphids are a serious problem in agriculture and plant resistance to these pests remains understudied. In general, aphids must manipulate the plant's defenses to establish a compatible relationship with the vascular system of their host, the phloem, and thus feed sustainably. This aphid strategy integrates the paradigm of plant-pathogen interactions which is based on the evolution of molecular patterns of pathogens recognized by NLR-type plant genes. Aphis gossypii is an extremely polyphagous aphid species with populations structured into host races specialized in different crops, including one specialized in cucurbits. In melon, the NLR Vat gene is unique since it confers both resistance to A. gossypii and to the viruses it transmits.

Surprisingly, the study of the diversity of the Vat/A. gossypii showed that the adaptation of aphids to NLR-like resistance by a polymorphism in a salivary effector is not the norm and raises the question of a potential diversity of adaptation pathways of A. gossypii to resistance NLR Vat. In an original way, A. gossypii could exploit the unique architecture of the melon vascular system, partitioned into two phloems with divergent properties to circumvent Vat resistance.
Through an approach based on the detection of metabolites highly representative of each of the two phloems of cucurbits, I have shown that clones of A. gossypii belonging to the host race specialized in cucurbits exploit the classic phloem when they feed on non-Vat melon and that the circumvention of Vat resistance by certain clones did not imply the use of the particular phloem of cucurbits.

In the frame of reference of plant-pathogen interactions, I aimed at identifying the salivary effector of A. gossypii which interacts with the melon VAT protein. Through comparative analysis of expression data of clones triggering or not triggering Vat resistance, I highlighted one candidate gene.