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Abstract

Oomycetes from the genus Phytophthora are plant pathogens, which have devastating impacts on agriculture and natural ecosystems. Phytophthora parasitica is a root pathogen with a hemibiotrophic lifecycle: during the initial stages of infection (biotrophy) the oomycete establishes an intimate contact with theliving cells of the host, before inducing plant cell death to complete its life cycle (necrotrophy). cDNA libraries that were obtained from P. parasitica-infected tomato plants and onion epidermis cells display severalsequences that encode secreted proteins with a canonical RxLR translocationsignal, such as Avh195. Avh195 possesses three potential binding sites for ATG8, a key protein in the process of autophagy. Heterologous expression ofAvh195 in tobacco plants slows down cell death responses such as those induced by proapoptotic BAX, and the HR inducers cryptogein and AvrPtoB. On this basis, we investigate the antagonism between death-inducing agents and Avh195 aiming at identifying the manipulated host signaling pathways, with a particular focus on the link between Avh195 and the autophagy machinery. To identify the molecular targets of Avh195, we initiated a trans-phylum analysis on plants, human cells, and green microalgae. Genetic expression of Avh195 dramatically alters the cellular phenotype in all these organisms, indicating that this protein targets an evolutionary-conserved mechanism.