Plant disease resistance (R) proteins play critical roles in plant immunity by directly or indirectly recognizing pathogen effectors, and lead to effector triggered immunity. Most of the R proteins are intracellular, and belongs to nucleotide binding (NB) domain and leucine-rich repeat (LRR)-containing (NLR) immune receptors. Besides those full length NLR immune receptors, there are many atypical NLRs that lack LRR domain in plant genome. Although those truncated NLR proteins are implicated in plant immunity, the function of those proteins are not well understood.

 

To study the mechanism of plant immune response, scientists in Dr. TANG Dingzhong’s lab from the Institute of Genetics and Developmental Biology, the Chinese Academy of Sciences, performed a mutant screen for enhanced disease resistance to powdery mildew. In this screen, Dr. TANG’s lab identified Arabidopsis exo70B1-3 mutant, which shows activated defense responses upon infection and express enhanced resistance to fungal, oomycete and bacterial pathogens.

 

EXO70B1 is one of the eight subunits of exocyst complex, which plays a critical role in exocytosis. In a screen for mutations that suppress exo70B1 resistance, they identified multiple alleles of a truncated NLR, TIR-NBS2 (TN2), suggesting that loss-of-function of EXO70B1 leads to activation of the TN2-mediated plant immunity. Significantly, they show that TN2 interacts with EXO70B1 in yeast and in planta.

 

Giving the important role of exocyst in plant immunity, this work suggests that pathogen effectors could evolve to target EXO70B1 to manipulate plant secretion machinery. And TN2 could monitor EXO70B1 integrity as part of an immune receptor complex. This work thus provides a mechanistic link between exocytosis and NLR function in plants, and sheds new lights on the plant immunity mediated by truncated NLRs.

 

This work entitled "A Truncated NLR Protein, TIR-NBS2, Is Required for Activated Defense Responses in the exo70B1 Mutant" has been published on PLoS Genetics (DOI:10.1371/journal.pgen.1004945), with Dr. ZHAO Ting, graduate student RUI Lu and Dr. LI Juan from Dr. TANG Dingzhong’s lab, as co-first authors.

 

This research was supported by grants from the Strategic Priority Research Program of the Chinese Academy of Sciences, National Basic Research Program of China, and National Natural Science Foundation of China.

 

 

 

 

Figure 8. EXO70B1 interacts with TN2 (Image by Ting Zhao etc.).