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Plant immune systems, like those of humans and animals, face a difficult balancing act: they must mount responses against ever-evolving pathogens, but they must not overdo it. An international group of plant biologists, including Frank Takken from the University of Amsterdam, has identified a crucial link in the process of how plants regulate their antiviral responses. The research is published in the March 2 issue of the Journal of Biological Chemistry.

The nucleus: a centre court for plant defence. The potato Rx1 immune receptor binds DNA, but it is unclear how this leads to defence. Here, we show that Rx1 has activity at chromatin by regulating DNA-binding of a Golden-2 like transcription factor, NbGlk1. Shown is a confocal image of Rx1-mCherry (orange) and GFP-NbGlk1 (green) co-expressed in Nicotiana benthamiana. Chloroplasts are pink.
The nucleus in Nicotiana benthamiana: a centre court for plant defence

Pathogens produce special proteins to manipulate their hosts and cause disease. So called NLR-receptors in plants can detect these proteins, resulting in the activation of an immune response halting the pathogen. So far, we had little knowledge of the molecules targeted by NLR-receptors to initiate immunity. In previous work the group demonstrated that NLR-receptors themselves can directly bind DNA. However, this work did not establish how an NLR-receptor could be targeted to the correct DNA sequences to establish an immune response.

Targeted response

Immune responses require energy and resources and often involve plants killing their own infected cells to prevent the pathogens from spreading. That is why it is of great importance that the immune response is only triggered when needed. The recent findings revealed an exciting, and unexpected, link between NLR receptors, plant DNA, and a specific class of DNA binding protein: the golden2-like transcription factors.

The golden2-like transcription factor named Glk1 binds to specific regions of DNA and activates genes involved in cell death and other plant immune responses. The team found that only when the Glk1 bound to a virus-activated  Rx1 NLR receptor, it was able to turn on the appropriate defence genes. Interestingly, when the viral protein was absent, Rx1 seemed to have the opposite effect – actually keeping Glk1 from binding to DNA. In this way, it prevented an inappropriate immune response.

Global food security

A mechanistic understanding of how plants resist or overcome pathogen attack is crucial to develop new strategies for crop protection.  Over 35% of global potential crop harvest is being lost to pathogens and pests, an amount that could feed 0.5-4 billion mouths. The underpinning science of plant immunity is therefore crucial to our food security agenda.

Growing crops that are resistant to pathogen attack, is considered the most environmental-friendly way to combat plant pathogens and to increase yield. Plant breeders cross in ‘resistance’ genes into elite varieties in a never-ending arms race to thwart newly emerging pathogens. But although used in practice, the knowledge on how these NLR-immune receptors encoded by resistance genes function stays behind. The follow up studies aim to further elucidate the mechanistic link between plant immunity and the action of NLR proteins at DNA to fully understand this mechanism.

About Frank Takken  

Frank Takken is associate professor in Molecular Plant Pathology at the UvA’s Swammerdam Institute for Life Sciences. In 2015 he received a Vici grant, one of the most substantial individual academic grants in the Netherlands. With this grant he conducts his research into pathogen-immunity in plants. He has a long-standing collaboration with Martin Cann, lead author on this publication and professor in the Department of Biosciences at Durham University (UK), and with Aska Goverse, assistant professor Nematology Wageningen University (NL).

Publication details

Philip D. Townsend, et. al. (2018). The intracellular immune receptor Rx1 regulates the DNA-binding activity of a Golden2-like transcription factor, The Journal of Biological Chemistry, Vol. 293, Issue 9, 3218-3233, March 2, 2018.

This publication was 'Editors pick' on 2 March. Editors’ Picks represent the top-rated papers published in the Journal of Biological Chemistry across the field of biological chemistry, as determined by the Associate Editors, Editorial Board Members and other referees.