An NB‐LRR protein required for HR signalling mediated by both extra‐ and intracellular resistance proteins

Abstract

SummaryTomato (Solanum lycopersicum) Cf resistance genes confer hypersensitive response (HR)-associated resistance to strains of the pathogenic fungus Cladosporium fulvum that express the matching avirulence (Avr) gene. Previously, we identified an Avr4-responsive tomato (ART) gene that is required for Cf-4/Avr4-induced HR in Nicotiana benthamiana as demonstrated by virus-induced gene silencing (VIGS). The gene encodes a CC-NB-LRR type resistance (R) protein analogue that we have designated NRC1 (NB-LRR protein required for HR-associated cell death 1). Here we describe that knock-down of NRC1 in tomato not only affects the Cf-4/Avr4-induced HR but also compromises Cf-4-mediated resistance to C. fulvum. In addition, VIGS using NRC1 in N. benthamiana revealed that this protein is also required for the HR induced by the R proteins Cf-9, LeEix, Pto, Rx and Mi. Transient expression of NRC1 D481V , which encodes a constitutively active NRC1 mutant protein, triggers an elicitor-independent HR. Subsequently, we transiently expressed this auto-activating protein in N. benthamiana silenced for genes known to be involved in HR signalling, thereby allowing NRC1 to be positioned in an HR signalling pathway. We found that NRC1 requires RAR1 and SGT1 to be functional, whereas it does not require NDR1 and EDS1. As the Cf-4 protein requires EDS1 for its function, we hypothesize that NRC1 functions downstream of EDS1. We also found that NRC1 acts upstream of a MAP kinase pathway. We conclude that Cf-mediated resistance signalling requires a downstream NB-LRR protein that also functions in cell death signalling pathways triggered by other R proteins.

The Effector SPRYSEC-19 ofGlobodera rostochiensisSuppresses CC-NB-LRR-Mediated Disease Resistance in Plants

“…The CC-NB-LRR protein NRC1 likely operates in signaling pathways downstream of different types of resistance proteins (e.g. Rx1, Mi-1.2, Cf4, and Cf-9; Gabriëls et al, 2007). To investigate whether SPRYSEC-19 modulates immune signaling downstream of resistance proteins, we coexpressed SPRYSEC-19 with an autoactive mutant of NRC1 (D481V) by agroinfiltration in leaves of N. benthamiana.…”

“…To investigate whether the SPRYSEC-19-induced suppression of CC-NB-LRR mediated programmed cell death involves a disturbed effector recognition, we coexpressed SPRYSEC-19 in N. benthamiana leaves with an autoactive Gpa2-Rx1 chimera (GG-GRR; Rairdan and Moffett, 2006), Mi-1.2 mutant [Mi-1.2(T557S); Gabriëls et al, 2007], and natural resistance gene homolog 10 from the H1 locus in potato (RGH10; FinkersTomczak et al, 2011). The transient coexpression of these proteins with 4MYC-GFP led to a local cell death response in agroinfiltrated leaf areas.…”

“…The following pairs of resistance genes and cognate elicitors were used to induce programmed cell death in leaves: Gpa2 / RBP1 (Sacco et al, 2009), Rx1 / cp106 (Slootweg et al, 2010), Cf4 / Avr4 (Thomas et al, 2000), Cf9 / Avr9 (Thomas et al, 2000), R3a / AvrR3a (Huang et al, 2005), Rpi-blb2 / AvrBlb2 , and BS4 (Schornack et al, 2005) / AvrBS4 (Ballvora et al, 2001). The following constructs of mutant CC-NB-LRR proteins were used to trigger an elicitor-independent programmed cell death: GG-GRR (Rairdan and Moffett, 2006), Mi-1.2(T557S) (Gabriëls et al, 2007), RGH10 , NRC1(D481V; Gabriëls et al, 2007), and INF1 (Kamoun et al, 2003). Agroinfiltrated leaves were monitored up to 10 d for visual assessment of cell death.…”

The wheat NB‐LRR gene TaRCR1 is required for host defence response to the necrotrophic fungal pathogen Rhizoctonia cerealis

“…Accumulating evidence indicates that plant NB‐LRR proteins not only act as immune receptors, but also contribute to signal transduction and/or amplification in plant–pathogens (Wu et al ., 2016). For example, the tomato NRC1, which was identified by combination techniques of cDNA‐amplified fragment length polymorphism and VIGS, functioned in cell death signalling pathways and contributed to resistance response to Cladosporium fulvum (Gabriëls et al ., 2007). We thus deduced that TaRCR1 might participate in defence signalling transduction and/or positive regulator.…”

“…Recently, an emerging model is that NB‐LRR proteins often function in pairs, with ‘helper’ proteins required for the activity of ‘sensors’ that mediate pathogen recognition (Bonardi et al ., 2011; Wu et al ., 2016). Certain NB‐LRR proteins contribute to signal transduction and/or amplification (Bonardi et al ., 2011; Césari et al ., 2014; Gabriëls et al ., 2007). The above‐mentioned NB‐LRRs play a pivotal role in plant resistance responses to biotrophic pathogens.…”