Abstract Detail

Molecular mechanisms of adaptation to host and environment

GIRALDO, MARTHA C. [1], Dagdas, Yasin [2], Gupta, Yogesh [2], Mentlak, Thomas [3], Yi, Mihwa [1], Martinez-Rocha, Ana Lilia [4], Saitoh, Hiromasa [5], Terauchi, Ryohei [5], Talbot, Nicholas J. [2], Valent, Barbara [1].

Two distinct mechanisms of Magnaporthe oryzae effector secretion for biotrophic invasion of rice.

Pathogens secrete effector proteins into host tissue to suppress immunity. Pathogenic bacteria have evolved several distinct secretion systems to target specific effector proteins during pathogenesis, but whether fungal pathogens require different secretory mechanisms is not clearly understood. We present evidence that the blast fungus Magnaporthe oryzae possesses distinct secretion systems for delivering effector proteins during biotrophic invasion of rice cells. M. oryzae secretes cytoplasmic effectors targeted for delivery inside rice cells and apoplastic effectors targeted to the extracellular space. Cytoplasmic effectors preferentially accumulate in the biotrophic interfacial complex (BIC), a plant derived structure located adjacent to the tip of the initially filamentous invasive hypha and then remaining next to the first differentiated bulbous invasive hypha cell. In contrast, apoplastic effectors remain in the extracellular compartment uniformly surrounding the invasive hypha inside the invaded cell. Disruption of the conventional ER-Golgi secretion pathway by Brefeldin A (BFA) treatment blocked secretion of apoplastic effectors, which were retained in the ER, but not secretion of cytoplasmic effectors. Fluorescence Recovery After Photobleaching experiments confirmed that cytoplasmic effectors continued to accumulate in BICs in the presence of BFA. Analysis of mutants showed that the BIC is associated with an unconventional form of secretion involving exocyst components, Exo70 and Sec5, and the t-SNARE Sso1, which are required for efficient delivery of effectors into plant cells and are critical for pathogenicity. By contrast, secretion of apoplastic effectors was not impaired in these mutants. These results revealed that effectors which function between the fungal cell wall and plant plasma membrane are secreted from invasive hyphae to the apoplast by the conventional ER-Golgi secretory pathway. We propose a model for a distinct secretory mechanism that the rice blast fungus has evolved for targeting cytoplasmic effectors to achieve tissue invasion.

1 - Kansas State University, Plant Pathology , 4024 Throckmorton Plant Science Center, Manhattan, KS, 66502, United States
2 - University of Exeter, School of Biosciences, Exeter, EX4 4QD, UK
3 - Cambridge Consultans Ltd, Cambridge, CB4 0DW, UK
4 - University of Hamburg, Department of Molecular Phytopathology and Genetics, Biozentrum Klein Flottbek, Hamburg, D-22609, Germany
5 - Iwate Biotechnology Research Center, Kitakami, Iwate, 024-0003, Japan

Keywords:
Effector
Secretion mechanisms
fungal plant pathogen.

Presentation Type: Symposium or Colloquium Presentation
Session: SY5
Location: Room 103 AB/Kellogg Hotel and Conference Center
Date: Tuesday, June 10th, 2014
Time: 3:00 PM
Number: SY5005
Abstract ID:68
Candidate for Awards:None