Abstract
Summary Plant immune receptors of the class of nucleotide‐binding and leucine‐rich repeat domain (NLR) proteins can contain additional domains besides canonical NB‐ARC (nucleotide‐binding adaptor shared by APAF‐1, R proteins, and CED‐4 (NB‐ARC)) and leucine‐rich repeat (LRR) domains. Recent research suggests that these additional domains act as integrated decoys recognizing effectors from pathogens. Proteins homologous to integrated decoys are suspected to be effector targets and involved in disease or resistance.Here, we scrutinized 31 entire plant genomes to identify putative integrated decoy domains in NLR proteins using the Interpro search. The involvement of the Zinc Finger–BED type (ZBED) protein containing a putative decoy domain, called BED, in rice (Oryza sativa) resistance was investigated by evaluating susceptibility to the blast fungus Magnaporthe oryzae in rice over‐expression and knock‐out mutants.This analysis showed that all plants tested had integrated various atypical protein domains into their NLR proteins (on average 3.5% of all NLR proteins). We also demonstrated that modifying the expression of the ZBED gene modified disease susceptibility.This study suggests that integration of decoy domains in NLR immune receptors is widespread and frequent in plants. The integrated decoy model is therefore a powerful concept to identify new proteins involved in disease resistance. Further in‐depth examination of additional domains in NLR proteins promises to unravel many new proteins of the plant immune system.
Highlights
In plants, disease resistance is frequently conferred by nucleotidebinding and leucine-rich repeat domain (NLR) proteins
Hypothetical integrated decoy domains are found in 15% of the cloned NLR R proteins
We retrieved the sequences of cloned R proteins and expertannotated R protein analogs of the NLR class from the Plant Resistance Gene Data Base (PRGdb) (Sanseverino et al, 2013; Table S4) and searched this data set of 98 NLRs for additional Interpro domains not present in canonical NLRs
Summary
Disease resistance is frequently conferred by nucleotidebinding and leucine-rich repeat domain (NLR) proteins. A third intermediate mode of effector recognition relies on the integration of decoy domains mimicking effector target proteins into NLRs (Cesari et al, 2014; Nishimura et al, 2015; Wu et al, 2015b). Integration of decoy domains was first suspected in poplar (Populus trichocarpa), where 32 NLR proteins were found to carry the same additional domain (Germain & Seguin, 2011). This additional domain, called BED (for BEAF and DREF Drosophila proteins containing this domain; Aravind, 2000), was found in nine rice (Oryza sativa) NLRs, including one that was found to code for the Xa1 functional resistance protein (Das et al, 2014). The authors of that study speculated about why both rice and poplar have independently acquired this gene architecture and raised the hypothesis that the integrated domain may act as a sensor for pathogen effectors
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