- © 2012 American Society of Plant Biologists. All rights reserved.
Abstract
Although the functions of a few effector proteins produced by bacterial and oomycete plant pathogens have been elucidated in recent years, information for the vast majority of pathogen effectors is still lacking, particularly for those of plant-pathogenic fungi. Here, we show that the avirulence effector AvrPiz-t from the rice blast fungus Magnaporthe oryzae preferentially accumulates in the specialized structure called the biotrophic interfacial complex and is then translocated into rice (Oryza sativa) cells. Ectopic expression of AvrPiz-t in transgenic rice suppresses the flg22- and chitin-induced generation of reactive oxygen species (ROS) and enhances susceptibility to M. oryzae, indicating that AvrPiz-t functions to suppress pathogen-associated molecular pattern (PAMP)-triggered immunity in rice. Interaction assays show that AvrPiz-t suppresses the ubiquitin ligase activity of the rice RING E3 ubiquitin ligase APIP6 and that, in return, APIP6 ubiquitinates AvrPiz-t in vitro. Interestingly, agroinfection assays reveal that AvrPiz-t and AvrPiz-t Interacting Protein 6 (APIP6) are both degraded when coexpressed in Nicotiana benthamiana. Silencing of APIP6 in transgenic rice leads to a significant reduction of flg22-induced ROS generation, suppression of defense-related gene expression, and enhanced susceptibility of rice plants to M. oryzae. Taken together, our results reveal a mechanism in which a fungal effector targets the host ubiquitin proteasome system for the suppression of PAMP-triggered immunity in plants.
Glossary
- PAMP
- pathogen-associated molecular pattern
- PRR
- pattern recognition receptor
- PTI
- PAMP-triggered immunity
- ROS
- reactive oxygen species
- ETI
- effector-triggered immunity
- HR
- hypersensitive response
- UPS
- ubiquitin proteasome system (
- NBS-LRR
- nucleotide binding site–Leu-rich repeat
- BIC
- biotrophic interface complex
- GFP
- green fluorescent protein
- NPB
- Nipponbare
- qPCR
- quantitative PCR
- qRT-PCR
- quantitative RT-PCR
- GST
- glutathione S-transferase
- DAI
- days after agroinfection
- Co-IP
- coimmunoprecipitation
- BiFC
- bimolecular fluorescence complementation
- RFP
- red fluorescent protein
- RNAi
- RNA interference
- TRD
- Toride
- CT
- cycle threshold
- Received September 19, 2012.
- Revised October 24, 2012.
- Accepted November 8, 2012.
- Published November 30, 2012.
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