image: NPR1 protein transitions between monomer and oligomer, and its oligomer further activates immunity. Overexpression of OsNPR1 in rice elevates broad-spectrum disease resistance but also causes growth and development defects; Piz-t confers race-specific resistance, it binds to and promotes OsNPR1 oligomerization, alleviating OsNPR1 monomer-induced growth defect phenotypes. Thus, pyramiding Piz-t and OsNPR1 OE further improved rice broad-spectrum disease resistance and eliminated side effects.
Credit: ©Science China Press
Plants have developed a set of defense mechanisms against pathogen infection. Basal immunity provides broad-spectrum resistance (BSR) but weak resistance to various pathogens, while resistance (R) gene mediated effector-triggered immunity (ETI) confers strong but race-specific resistance to limited pathogens. NPR1 is a positive regulator of plant basal immunity. Although overexpression of NPR1 enhances immunity in various crops, these overexpression plants showed growth defects and yield losses, posing challenges for the application of NPR1 in crop improvement.
R gene Piz-t confer full resistance to many Magnaporthe oryzae isolates and have been incorporated in elite rice varieties. Dr. Ning and colleagues found that OsNPR1 interacts with Piz-t. Knocking out of OsNPR1 resulted in susceptibility, but is not sufficient to destroy Piz-t-mediated resistance. They then generated the Piz-t×OsNPR1OE hybrid rice by crossing the Piz-t with OsNPR1 OE plants. These hybrid rice plants are fully resistant to Piz-t incompatible strain and are more resistant to Piz-t compatible strain, as well as enhances resistance to Xanthomonas oryzae pv. oryzae (Xoo).
The Piz-t×OsNPR1OE plants also showed alleviated growth defects phenotype. Although the OsNPR1 transcript and total protein are not changed between OsNPR1 OE and Piz-t×OsNPR1OE plants, the monomer form of OsNPR1 was significantly reduced in Piz-t×OsNPR1OE plants. Dr. Ning and colleagues further identified key amino acids involved in OsNPR1 dimerization. Mutation of these sites on OsNPR1 block protein dimerization and their transgenic overexpression plants have almost lost the resistance, while they still show a growth defect phenotype. Therefore, Piz-t optimizes OsNPR1-mediated immunity and alleviates OsNPR1-triggered growth defects by converting OsNPR1 monomers to oligomers.
In addition, Dr. Ning and colleagues generated OsNPR1 OE plants in 07GY31-Piz-t, a rice breeding material, validating the strong disease resistance conferred by Piz-t and OsNPR1 OE without obvious growth defect phenotype. This work therefore provided an important reference for how to applicate NPR1 in resistance breeding and new insights into the feasibility of pyramiding basal immunity and ETI in other crops.
Dr. Feng He, a joint postdoctoral fellow of IPPCAAS and the Agricultural Genomics Institute, is the first author of the paper. Prof. Yuese Ning (IPPCAAS) is the corresponding author. The project was supported by grants from the National Key Research and Development Program of China, the National Natural Science Foundation of China, the Innovation Program of Chinese Academy of Agricultural Sciences and the China Postdoctoral Science Foundation.
Journal
Science Bulletin