Evolution of Innate Immunity: Lessons from Arabidopsis and C. elegans.

Fred Ausubel, Department of Genetics, Harvard Medical School and Department of Molecular Biology, Massachusetts General Hospital

The innate immune response appears to have ancient evolutionary origins as suggested by common features of the innate immune response in vertebrates, invertebrate animals, and plants including defined receptors for microbe-associated molecules, conserved MAPK signaling cascades, and the production of anti-microbial peptides. It remains to be determined, however, whether the similarities in innate immunity represents a process of divergent evolution from an ancient unicellular eukaryote or convergent evolution that selects from a limited set of conserved regulatory modules. Innate immune signaling is highly conserved between insects and mammals but only a few components of the insect/mammalian immune signaling pathways are also conserved in plants and nematodes. Plants and nematodes are similar in that neither have dedicated immune cells and that both appear to have multiple parallel and apparently independent immune response pathways. In Arabidopsis, the immune pathways downstream of PAMP receptors do not require the secondary signaling molecules salicylic acid, jasmomic acid or ethylene. In C. elegans, the PMK-1 p38 MAPK pathway and the DAF-2/DAF-16 insulin signaling pathway control immunity, but there is essentially no overlap between immune effectors positively regulated by PMK-1 and DAF-16.