The repetitive Ustilago maydis effector Rsp3 shields hyphae and blocks the anti-fungal activity of a secreted maize protein
L. MA (1), C. Trippel (1), L. Wang (2), A. Mendoza-Mendoza (3), S. Ullmann (4), M. Moretti (1), S. Wawra (1), S. Reissmann (1), K. Münch (1), B. Zechmann (5), R. Kahmann (1) (1) Max Planck Institute for Terrestrial Microbiology, Germany; (2) Max Planck Institute for Heart and Lung Research, Germany; (3) Bio-Protection Research Centre, New Zealand; (4) Heinrich-Heine-Universität Düsseldorf, Germany; (5) Center for Microscopy and Imaging (CMI), Baylor University, U.S.A.

The biotrophic fungus Ustilago maydis causes smut disease in maize. Hallmarks of the disease are plant tumors and anthocyanin biosynthesis. Here we functionally characterize the secreted effector Rsp3 which contains several repetitive as well as a Cys-rich domain. rsp3 alleles obtained from field isolates have full biological activity but differ in size and this is caused by reduced or expanded numbers of certain repeats. rsp3 is highly expressed during the biotrophic stage and is required for virulence and anthocyanin accumulation. Rsp3-HA can be easily detected in culture supernatants when expressed from a constitutive promoter, but displays highly anomalous migration behavior on SDS-PAGE. During biotrophic growth Rsp3 decorates the surface of biotrophic hyphae inside infected plant tissue. Using immunoprecipitation and mass spectrometry, we show that Rsp3 interacts with maize DUF26 domain-family proteins. When expressed and purified from Nicotiana benthamiana the interacting maize DUF26 domain protein showed antifungal activity against the U. maydis rsp3 deletion mutant but not against a strain over-expressing rsp3. This suggests that the Rsp3 effector blocks the antifungal activity of the DUF26-containg maize protein, presumably by inhibiting its binding to the fungal cell wall.

Abstract Number: C20-5, P6-151
Session Type: Concurrent