Thursday, January 14, 2016
Pairs and decoys in plant immune receptors
INRA, UMR BGPI, Montpellier, France
Plant diseases are among the most serious problems in agriculture and the use of plant immunity controlled by disease resistance (R) genes is a key strategy for crop protection. The vast majority of R genes code for NLR multi domain proteins that are characterized by nucleotide-binding and leucine-rich repeat domains and that act as intracellular immune receptors recognizing pathogen-secreted virulence factors termed effectors. NLR proteins may be sufficient for both effector recognition and signaling activation or act in pairs where two different NLR proteins are required to confer resistance to pathogens. Recent detailed studies on the rice NLR pair RGA4/RGA5 has revealed how such NLR pairs function together1,2: 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 effectors 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 a C-terminal, uncommon domain of RGA5 that shows similarity to the copper chaperone ATX1 from Saccharomyces cerevisiae and that we named RATX1 (related to ATX1) domain. 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 receptor3. Similar interactions have been described for the Arabidopsis thaliana NLR pair RRS1 and RPS4 highlighting a conserved mode of action of NLR pairs across both monocotyledonous and dicotyledonous plants. I will show recent data that further support the ‘integrated decoy model’ and that uncover advantages of this mode of recognition.
1 Cesari, S. et al. The rice resistance protein pair RGA4/RGA5 recognizes the Magnaporthe oryzae effectors AVR-Pia and AVR1-CO39 by direct binding. Plant Cell 25,1463–81 (2013).
2 Césari, S. et al. The NB-LRR proteins RGA4 and RGA5 interact functionally and physically to confer disease resistance. EMBO J. 33,1941–1959 (2014).
3 Cesari, S., Bernoux, M., Moncuquet, P., Kroj, T. & Dodds, P. N. A novel conserved mechanism for plant NLR protein pairs : the ‘integrated decoy’ hypothesis. Front. Plant Sci.5,577 (2014).
Contact : Przemyslaw Bidzinski