The molecular dialog between oomycete effectors and their plant and animal hosts

Oomycetes form a phylogenetically distinct group of eukaryotic microorganisms that include some of the most notorious pathogens of plants and animals. Through the deployment of a remarkably diverse array of effector proteins, oomycete pathogens succeed to overcome host defences and cause infection. Effectors can operate extracellularly or enter living cells where they target diverse subcellular compartments. Genome sequence information indicates that oomycetes express several hundred host-translocating effectors potentially targeting a myriad of host processes. To counteract, plants rely on a wide variety of extra- and intracellular immune receptors facilitating pattern-triggered and effector-triggered immunity, respectively. Similarly, effectors from animal pathogenic oomycetes also target host immune response pathways, which in turn causes the activation of the humoral and adaptive immune system. In this review, we compare plant and animal pathogenic oomycete effectors regarding their type, function, genetic diversity, as well as host responses.