New light on innate plant immunity
Plants are able to resist a pathogen’s attack by a dual innate immune system. The relationship between the two pathways was not clear, but it turns out that they mutually potentiate each other, as assistant professor Pingtao Ding (Institute of Biology Leiden) and colleagues (The Sainsbury Laboratory, UK) show in Nature.
Microbial plant pathogens are opposed by plants. As a general defence, plants possess an innate immune system. It was known to consist of two pathways, the interaction of which was not clear. Now, Pingtao Ding and colleagues discovered that they act as one, integrated whole. The pathways only function well when both are activated.
Two lines of defence
The first pathway of the innate immune system is triggered when receptors on the surface of plant cells recognise certain molecular patterns of pathogens, such as viruses, bacteria, and fungi. Activation results in the production of damaging oxygen species that may restrict the growth of the pathogen. A pathogen that survives this first line of defence will excrete molecules into plant cells that are recognised by internal receptors of the plant. They trigger the second immune pathway, which may result in destruction of infected cells when strongly activated.
‘Until now, the second or internal immunity pathway has not been investigated on its own, as in practice, it is only activated when the first pathway is too’, Ding tells. ‘Also, interactions between these two pathways were poorly understood.’ So, he decided to artificially stimulate either the cell-surface receptors, or the internal receptors, or both, in order to induce each immune pathway solely or both together and to study their separate effects.
But there are no separate effects, as it turned out. Instead, both pathways strongly interact. Stimulation of internal receptors has no effect unless cell-surface receptors are stimulated too. And the effect of stimulating cell-surface receptors will extinguish soon unless internal receptors are triggered as well; in that case, the effect of triggering cell-surface receptors is boosted: it will be stronger and of longer duration. Ding: ‘The pathways need each other’s activation to function, and they potentiate each other. Their effects partly overlap. For instance, both result in the production of damaging reactive oxygen species. As a result, plants are able to mount a strong defensive response upon attack by a pathogen. This new knowledge is relevant to strategies for increasing the resistance of crops to diseases.’
New in Leiden
Ding used the model plant Arabidopsis thaliana and the bacterial plant pathogen Pseudomonas syringae and conducted the research at the Sainsbury Laboratory and University of East Anglia in Norwich, UK. On 1 April, he will start a new position as an assistant professor at the Institute of Biology Leiden. ‘My expertise fits perfectly within the institute’s research lines, so I will continue my work on plant immunity in Leiden. While the Nature paper delivers a fairly simple message as the main point of the discovery, it has opened many new questions, challenges, and opportunities to follow up.’
Ngou, B.P.M., H-K. Ahn, P. Ding & J.D.G. Jones, 2021. Mutual potentiation of plant immunity by cell-surface and intracellular receptors. Nature, online on 10 March.
Text: Willy van Strien