Plant pathogens deliver effector proteins into plant host cells to increase infectivity by modifying or removing protective host proteins. Plants detect effector proteins via NLR immune receptors which monitor host effector targets. In response to effector target tampering, NLRs potentiate immunity. The guard hypothesis thus proposes that NLRs ‘guard’ host ‘guardees’. A corollary to this is that autoimmunity in plants may be due to inappropriate NLR activation and not caused by mutations in negative regulators of immunity as described in many highly cited research papers.
We therefore developed a novel, rapid suppressor screen based on specific Dominant Negative (DN-NLR) mutations in a conserved NLR domain. This screen confirmed that autoimmunity in many mutants require NLRs. Since we can now remove the effects of the triggered NLR guard(s), we can properly ask three important questions:
1 – What are the true functions of the guardee proteins?
2 – Why are they guarded?
3 – How can we exploit them to increase plant production?