Paired NLRs and integrated decoy domains in rice blast resistance
Diana Ortiz1, Stella Césari1, Veronique Chalvon1, Karine de Guillen2, Andre Padilla2, Jean Benoit Morel1, Thomas Kroj1.
1 INRA, Biology and Genetics of Plant-Pathogen Interactions Laboratory - BGPI, Montpellier, France
2 CNRS/INSERM, Centre de Biochimie Structurale – CBS, Montpellier, France
Disease resistance (R) genes are key element of plant immunity and crucial for resistance breeding in crops. The vast majority of R genes code for NLR multi domain proteins characterized by nucleotide- binding and leucine-rich repeat domains. NLRs act as intracellular immune receptors recognizing pathogen-secreted virulence factors termed effectors and, frequently, two different NLR proteins are required to confer resistance to pathogens.
Recent studies on the rice NLR pair RGA4/RGA5 responsible for Pia and PiCO39 resistance have revealed how such NLR pairs function together (1, 2): the paired partners RGA4 and RGA5 interact physically to form a hetero-complex receptor in which each partner plays distinct roles in effector recognition or signaling activation. RGA5 acts as a receptor that binds directly to the structurally conserved effectors AVR-Pia and AVR1-CO39 of the fungal rice pathogen Magnaporthe oryzae while RGA4 acts as a constitutively active signaling protein that is repressed by RGA5 in the absence of effectors. Effector-binding is mediated by an integrated C- terminal, uncommon domain of RGA5 with similarity to copper chaperones (RATX1 domain for related to ATX1). To understand this kind of effector recognition, we propose an ‘integrated decoy’ model that states that the RATX1 receptor domain resembles to targets of the recognized effectors and therefore acts as a decoy that has been integrated into NLR proteins to create a versatile pathogen receptor (3).
Our analysis of 31 entire plant genomes showed that integration of uncommon potential decoy domains in NLR immune receptors is widespread and frequent (4). All tested plants have integrated various, atypical protein domains into their NLR proteins with a mean frequency of 5%. The integrated decoy model is therefore a powerful concept for the identification of novel players in disease resistance since further in-depth examination of integrated domains in NLRs promises to identify many new immunity-related proteins.
1. S. Cesari et al., Plant Cell. 25, 1463–81 (2013). 2. S. Césari et al., EMBO J. 33, 1941–1959 (2014). 3. S. Césari et al., Front. Plant Sci. 5, 577 (2014). 4. T. Kroj et al., New Phytol. 210, 618–626 (2016).
