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Dissection of cell death induction by wheat stem rust resistance protein Sr35 and its matching effector AvrSr35.

  • Author(s): Bolus, Stephen
  • Akhunov, Eduard
  • Coaker, Gitta
  • Dubcovsky, Jorge
  • et al.

Nucleotide-binding leucine-rich repeat receptors (NLRs) are the most abundant type of immune receptors in plants and can trigger a rapid cell death (hypersensitive) response upon sensing pathogens. We previously cloned the wheat NLR Sr35, which encodes a coiled-coil (CC) NLR that confers resistance to the virulent wheat stem rust race Ug99. Here, we investigated Sr35 signaling after Agrobacterium-mediated transient expression in Nicotiana benthamiana. Expression of Sr35 in N. benthamiana leaves triggered a mild cell death response, which is enhanced in the auto-active mutant Sr35 D503V. The N-terminal tagging of Sr35 with GFP blocked the induction of cell death, whereas a C-terminal GFP tag Sr35 did not. No domain truncations of Sr35 generated cell death responses as strong as the wild-type, but a truncation including the CC-NB-ARC domains in combination with the D503V auto-active mutation triggered cell death. In addition, co-expression of Sr35 with the matching pathogen effector protein AvrSr35 resulted in robust cell-death and electrolyte leakage levels that were similar to auto-active Sr35 and significantly higher than Sr35 alone. Co-expression of Sr35-CC-NB-ARC and AvrSr35 did not induce cell death, confirming the importance of the LRR for AvrSr35 recognition. These findings were confirmed through Agrobacterium-mediated transient expression in barley. Taken together, these results implicate the CC-NB-ARC domains of Sr35 in inducing cell death and the LRR domain in AvrSr35 recognition.

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