A Malaria Type Effector in the Soybean Cyst Nematode Modulates the Plant Immune System
Cyst nematodes (CNs) are sedentary endoparasitic round worms that infect the roots of economically important plants such as soybean, potato and sugar beet. CNs secrete proteins (effectors) into root tissues and cells to promote parasitism. Sequence analyses of one CN effector determined that it has marginal, but significant similarity to an effector found only in the Malaria parasites (Plasmodium spp.), the Circumsporozoite Protein (CSP). Furthermore, the CN effector and Plasmodium CSPs share four protein domains that are essential for CSP function inside animal cells. Numerous evidences indicate that Plasmodium CSPs suppress the immune systems of their animal hosts by multiple, diverse strategies. As plants have immune systems, with significant overlaps with the animal innate immune system, we performed assays to test whether the CN effector suppresses plant immunity. Remarkably, multiple lines of evidence indicate that the CN effector strongly suppresses both of the major routes of the plant immune system. We are currently testing whether a CSP from the monkey Malaria species, P. fieldi, which the CN effector is most similar to, also suppresses plant immunity. We hypothesize that the CN effector and CSPs have converged on similar sequences to execute similar functions in their plant and animal hosts, respectively.