Characterization of effector candidates from the soybean rust fungus that suppress plant immunity
M. QI (1), T. Link (2), R. Voegele (3), T. Baum (1), S. Whitham (1) (1) Iowa State University, U.S.A.; (2) Institut für Phytomedizin, Universität Hohenheim, Germany; (3) Institut für Phytomedizin, Universität Hohenheim, Germany

Soybean rust (SBR) is an important disease caused by Phakopsora pachyrhizi (Pp). Like other rust fungi, Pp forms specialized cells called haustoria, which are key hubs of molecular exchange with host cells. Haustoria express effector proteins that are transferred to plant cells where they promote fungal growth. We have recently sequenced the Pp haustorial transcriptome and predicted candidate effector proteins. To gain insights into functions of Pp effector candidates (PpECs), we have cloned 82 PpEC coding sequences and delivered the proteins into host and non-host plants using a bacterial type III secretion system-based delivery vector. Several PpECs suppressed immune responses associated with effector- and pattern-triggered immunity, and we are in the process of characterizing these further. One interesting example is PpEC23, a small, cysteine-rich effector candidate that attenuated the hypersensitive response caused by Pseudomonas syringae pv tomato DC3000 on soybean and tobacco, and it also suppressed basal defense on tobacco and Arabidopsis. PpEC23 interacts with a transcription factor that our data suggests negatively regulates soybean defenses. We are now using host-induced gene silencing and transcriptomics to determine the effects of PpEC23 and the interacting soybean transcription factor in immunity or virulence. The results are expected to provide mechanistic insights into the molecular basis of SBR and may be relevant to other rust diseases.

Abstract Number: P9-296
Session Type: Poster