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Thesis started, 2014 - Defended in december 15^th 2017
Fund:  INRA - Région Bretagne
Direction: Akiko Sugio, Jean-Christophe Simon

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Abstract

Effector molecules play fundamental roles in antagonistic plant-pathogen interactions mainly by suppressing plant defense and allow parasites to reproduce and multiply on the plant. Recently, some effectors have been characterized in herbivorous insects; however, their contribution to the evolution of plant specialization in insects remains largely unknown. Aphids feed from phloem sap and inject salivary proteins, some of which are known to act as effectors into the host plant. Studying evolutionary patterns and characterizing functions of effectors appear as important steps toward unveiling the mechanisms of host plant specialization in aphids. The pea aphid, Acyrthosiphon pisum, is specialized to legumes and has experienced multiple events of specialization resulting in a large complex of biotypes. This work sought to identify salivary effectors that are involved in pea aphid adaptation to its hosts by taking both evolutionary and functional approaches starting from creation of a new catalogue of putative effectors. A transcriptomic analysis identified 740 putative effectors that are up-regulated in salivary glands of A. pisum, and comparative genomics on newly sequenced aphid genomes revealed that some of them evolve rapidly. Moreover, salivary gene family expansion, allowing diversifying selection of certain gene copies, appears as an important source of novel effectors in A. pisum. In parallel, this work optimized Agrobacterium-mediated transient gene expression in pea to provide a new tool for functional analyses of pea aphid effectors. The construction of a comprehensive catalogue of A. pisum salivary effectors and evolutionary analysis of them provide new candidates in host plant adaptation. By using the gene expression tool now available in pea, functional characterization of candidates will help to identify the effectors that are involved in plant specialization in the pea aphid complex. 

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