2011
Mol Biol Evol. 2012 Apr;29(4):1263-76
29 Apr 2012 Highly dynamic exon shuffling in candidate pathogen receptors… What if brown algae were capable of adaptive immunity?Antonios Zambounis, Marek Elias, Lieven Sterck, Florian Maumus, Claire M.M. Gachon
Pathogen recognition is the first step of immune reactions. In animals and plants, direct or indirect pathogen recognition is often mediated by a wealth of fast-evolving receptors, many of which contain ligand-binding and signal transduction domains, such as leucine-rich or tetratricopeptide repeat (LRR / TPR) and NB-ARC domains, respectively. In order to identify candidates potentially involved in algal defence, we mined the genome of the brown alga Ectocarpus siliculosus for homologues of these genes, and assessed the evolutionary pressures acting upon them. We thus annotated all Ectocarpus LRR-containing genes, in particular an original group of LRR-containing GTPases of the ROCO family, and 24 NB-ARC-TPR proteins. They exhibit high birth and death rates, whilst diversifying selection is acting on their LRR (respectively TPR) domain, probably affecting ligand-binding specificities. Remarkably, each repeat is encoded by an exon, and intense exon shuffling underpins the variability of LRR and TPR domains. We conclude that the Ectocarpus ROCO and NB-ARC-TPR families are excellent candidates for being involved in recognition / transduction events linked to immunity. We further hypothesize that brown algae may generate their immune repertoire via controlled somatic recombination, so far only known from vertebrate adaptive immune systems.
Creation date: 18 Dec 2011
eZ PublishPublication supervisor: A-F. Adam-Blondon
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