A Stress Response Kinase Cascade Is Conserved in Arabidopsis and Modulated by a Parasite Effector

We report that a novel <i>Arabidopsis thaliana</i> kinase cascade shows telltale similarities to the kinase cascades of oxidative stress response kinases (OSRKs) from humans and animals. A previously uncharacterized <i>A. thaliana</i> OSRK-like serine/threonine protein kinase (AtOSRK1) physically interacts with the kinase 'With No Lysine' Kinase 5 (WNK5) and the plasma membrane-bound SNARE protein AtSYP132. The physical interaction between AtOSRK1 and AtWNK5 is governed by conserved domains also found in animal proteins; however, in all plants assayed, one of the interaction domains is found in the opposite kinase when compared with human/animal counterparts. We show that AtOSRK1 and AtWNK5 are members of a kinase cascade in which AtWNK5 phosphorylates and activates AtOSRK1, and both kinases then phosphorylate syntaxin AtSYP132. Homologous human/animal proteins have been shown to function in a strikingly similar fashion in stress responses and are involved in known inherited hypertensive disease states. We show that a novel effector protein (Hs28B03) of the plant-parasitic cyst nematode <i>Heterodera schachtii</i> specifically targets AtOSRK1 and interferes with the <i>A. thaliana</i> kinase cascade, resulting in a suppression of the phosphorylation of AtSYP132. <i>A. thaliana</i> lines constitutively expressing the <i>Hs28B03</i> coding sequence showed elevated susceptibility to the cyst nematode while also exhibiting larger size, suggesting suppressed defense in favor of vegetative growth. These findings document a functional <i>A. thaliana</i> protein kinase cascade that is structurally and functionally conserved in plants and humans/animals. Furthermore, the manipulation of this kinase cascade by a parasite effector revealed a novel mechanism of parasitism influencing growth-defense tradeoffs.