Two Studies Reveal Steps in Plant Immune Receptor Activation

Two studies conducted in the laboratory of Alexander von Humboldt Professor Jijie Chai at the Max Planck Institute for Plant Breeding Research provide unprecedented structural insight into how plant immune receptors are primed and activated to provide plants with resistance against microbial pathogens.

An important plant mechanism is defined by cytoplasmic receptors called NLRs that recognize effectors, the molecules that invading microorganisms secrete into the plant's cells. These recognition events can either involve direct recognition of effectors by NLRs or indirect recognition, in which the NLRs act as ‘guards' that monitor additional host proteins or ‘guardees' that are modified by effectors.

The studies by Jijie Chai together with research teams from Tsinghua University and the Chinese Academy of Sciences have now pieced together the sequence of molecular events that convert inactive NLR molecules into active complexes that provide disease resistance.

The researchers looked at the protein called ZAR1, an ancient plant molecule capable of indirectly sensing several unrelated bacterial effectors. They observed that in the absence of bacterial effectors, ZAR1, together with RKS1, stays in a latent state through interactions involving multiple domains of the ZAR1 protein. Upon infection, a bacterial effector modifies the plant ‘guardee' PBL2, which then activates RKS1 resulting in huge conformational changes that first allow plants to swap ADP for ATP and then result in the assembly of a pentameric, wheel-like structure that the authors term the ‘ZAR1 resistosome'.

For more details, read the news release from Max Planck Institute for Plant Breeding Research.