Effector-triggered defence: A new concept in plant pathogen defence

In June, a team of Brassica researchers from the University of Hertfordshire proposed a new classification for a type of plant defence mechanism: effector-triggered defence (ETD).

Henrik Stotz is first author of the paper describing ETD, currently In Press in Trends in Plant Science. He explains, “In the same way that humans have developed immune responses against human disease pathogens, crops can be bred for resistance against disease pathogens, but we need to improve our understanding of effective resistance mechanisms within plants. Our research enhances the traditional understanding of the plant defence system and describes a new concept, which is how plants protect themselves against the pathogens that grow in the space outside plant cells (the apoplast) – a new concept called effector-triggered defence or ETD.”

Traditionally, plant pathogen defence is broken into two broad forms: pathogen-triggered immunity (PTI) and effector-triggered immunity (ETI). PTI is the first action the plant takes against a pathogen and is triggered when the pathogen lands on the plant. The pathogen releases molecules called effectors into the plant cells, which the plant recognises and reacts against. If the effectors are not recognised, the pathogen can spread with little resistance.

The team from Hertfordshire, led by Bruce Fitt, argue that one line of defence, R gene-mediated host resistance against fungal pathogens that grow in the space between cells, is not adequately explained by either mechanism.

Effector-triggered defence (ETD) is mediated by R genes encoding cell surface-bound receptor-like proteins that engage the receptor-like kinase SOBIR1 – an extracellular recognition. The response is host cell death after an extended period of endophytic pathogen growth. This is in contrast to ETI, in which detection of the pathogen occurs within cells and usually triggers fast host cell death.

ETD is described in Stotz et al. (In Press) Trends in Plant Science DOI: http://dx.doi.org/10.1016/j.tplants.2014.04.009

The quotes used in this article are from this BBSRC Press Release. This story was originally posted on the UK Brassica Research Community website.


NGS and root endophyte assembly cues

Cologne and Sanssouci, close to Golm: what effect do the soils at these two historic locations have on the local plant roots?

Highlighted article: Davide Bulgarelli, Matthias Rott, Klaus Schlaeppi, Emiel Ver Loren van Themaat, Nahal Ahmadinejad, Federica Assenza, Philipp Rauf,  Bruno Huettel, Richard Reinhardt, Elmon Schmelzer, Joerg Peplies, Frank Oliver Gloeckner, Rudolf Amann, Thilo Eickhorst, and Paul Schulze-Lefert (2012) Revealing structure and assembly cues for Arabidopsis root-inhabiting bacterial microbiota Nature 488:91


Although plant-microbe and plant-soil dynamics are widely studied areas of plant science, up until now there has been no broad picture of plant endophytic systems: which phyla are common endophytes; how the populations form; and what affects them. Endophytes colonise plant tissues, where unlike pathogens they do not cause harm or an immune response, and unlike endosymbionts they do not live inside plant cells or have an obvious mutually beneficial relationship with the plant. A recent review on bacterial endophytes is this one by Reinhold-Hurek and Hurek (2011).

Here, Bulgarelli et al. use an Arabidopsis system to shed light on the specifics of below ground plant-bacteria interactions, and set out a methodology for future investigations into other plants and soil types. This study and another article in the same issue of Nature by Lundberg et al. use next generation sequencing (NGS) to show similar cues for assembly of root endophytes. (more…)

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