Suppression or activation of immune responses by predicted secreted proteins of the soybean rust pathogen Phakopsora pachyrhizi

Authors: QI, MINSHENG - Iowa State University; GRAYCZYK, JAMES - Iowa State University; SEITZ, JANINA - Hohenheim University; YOUNGSILL, LEE - Seoul National University; LINK, TOBIAS - University Of Hohenheim; CHOI, DOIL - Seoul National University; Pedley, Kerry; VOEGELE, RALF - University Of Hohenheim; BAUM, THOMAS - Iowa State University; WHITHAM, STEVEN - Iowa State University

Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2017
Publication Date: 1/1/2018
Publication URL: http://handle.nal.usda.gov/10113/5922784
Citation: Qi, M., Grayczyk, J.P., Seitz, J.M., Youngsill, L., Link, T.I., Choi, D., Pedley, K.F., Voegele, R.T., Baum, T.J., Whitham, S.A. 2018. Suppression or activation of immune responses by predicted secreted proteins of the soybean rust pathogen Phakopsora pachyrhizi. Molecular Plant-Microbe Interactions. 31:163-174.

Interpretive Summary: Fungal plant pathogens known as the “rust fungi” are major threats to crop production. During the infection process, rust fungi form specialized structures that enable them to acquire nutrients from the host plant. These structures are also important for the delivery of proteins, known as effectors, into the plant. Many effectors likely play a role in suppressing plant immune responses, thus enabling the pathogen to infect the host. Although many hundreds of candidate effector proteins have been identified from rust fungi, experimental evidence demonstrating their functions is lacking. In this study, we used several experimental approaches to characterize 82 effector proteins from a rust pathogen that infects soybean. This work provides a foundation for future studies that may allow better control of plant diseases caused by rust fungi that impact crop production.

Technical Abstract: Rust fungi, such as Phakopsora pachyrhizi, are major threats to crop production. They form specialized haustoria that are intimately associated with plant cells. These haustoria have roles in acquiring nutrients and secreting effector proteins that manipulate host immune systems. Functional characterization of effector proteins of rust fungi is important for understanding mechanisms that underlie their virulence and pathogenicity. Hundreds of candidate effector proteins have been predicted for rust pathogens, but it is not clear how to prioritize these effectors candidates for further characterization. There is a need for high-throughput approaches for screening effector candidates in order to obtain experimental evidence for effector-like functions, such as the manipulation of host immune systems. We have focused on identifying effector candidates with immune related functions in the soybean rust fungus, P. pachyrhizi. To facilitate screening many P. pachyrhizi effector candidates (PpECs), we used heterologous expression systems including the bacterial type III secretion system, Agrobacterium infiltration, a plant virus, and yeast to establish an experimental pipeline for identifying PpECs with immune related functions and establishing their subcellular localizations. Several PpECs (17 of 82 tested) were identified that could suppress or activate immune responses in non-host N. benthamiana, Arabidopsis, tomato, or pepper plants.