We report that a novel Arabidopsis thaliana kinase cascade shows telltale similarities to the kinase cascades of oxidative stress response kinases (OSRKs) from humans and animals. A previously uncharacterized A. thaliana 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 Heterodera schachtii specifically targets AtOSRK1 and interferes with the A. thaliana kinase cascade, resulting in a suppression of the phosphorylation of AtSYP132. A. thaliana lines constitutively expressing the Hs28B03 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 A. thaliana 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.
Juvale et al. (Wed,) studied this question.