ERC Grant to test the green beard effect in plants

The number of offspring a plant produces depends on its neighbours, which may, for example, capture light and soil nutrients before it can. Several studies suggest that plants are able to adjust their response to neighbouring plants according to their genetic identity, in particular by favouring relatives through reduced root competition, reduced shading or warning signals when an herbivore arrives. These findings remain a matter of debate, however, because the mechanisms that could enable such recognition are still largely unknown at both genetic and molecular level.

A gene that recognises its own kind 

How can an organism recognise a relative without knowing it? Germain Montazeaud is exploring a process first described by biologist William Hamilton and later popularised by Richard Dawkins: the “green beard” effect. A single gene — or a small number of closely linked genes in the genome — are thought to perform three functions at once: produce a recognisable signal, detect that signal in others, and favour individuals that carry it, even when they are otherwise unrelated across the rest of the genome. “These genes cause the individuals that carry them to favour others with the same version of the gene. In a sense, they use interactions between individuals to spread,” explains Germain Montazeaud.

The effect has since been observed in insects, with the best-known example being fire ants, in which workers kill queens carrying a different version of the gene. No green beard has ever been identified in plants. Over the past 20 years, research on kin recognition in plants — the idea that a plant treats its relatives differently because they are similar across the genome as a whole — has attracted most of the attention, leaving other possibilities such as the green beard effect, where only one specific gene matters, largely unexplored. “The project aims to move beyond the current controversies surrounding communication and recognition between plants by looking for mechanisms whose genetic and molecular basis we can describe precisely,” says Germain Montazeaud.

Crossing disciplinary as well as conceptual boundaries

Why has this avenue remained unexplored? “The main obstacle is the disciplinary divide. Plant biologists are not very familiar with theories of cooperation and social evolution, which have mainly been developed and applied to animals,” explains Germain Montazeaud. There is also a more conceptual barrier: the idea that social behaviour requires some form of consciousness. “We tend to think that social traits only evolve in organisms with a nervous system. That is not the case: green beard genes exist in microorganisms, including bacteria.”

“Plants already have the necessary machinery,” the researcher points out. In around 40% of flowering plant species, systems exist that can recognise the genetic identity of pollen and prevent self-fertilisation: a small number of closely linked genes combine the production of a signal with recognition of that signal. “This process bears striking similarities to a green beard effect. It leaves open the possibility that genes of this kind may have evolved in plants.”

One thousand genotypes to explore the genome

Research to date has relied on a small number of genotypes — naturally occurring genetic variants of the same plant — making it difficult to distinguish a genuine effect of relatedness from simple differences in growth. With ERC funding, PHYTOPOGON can work on a much larger scale and adopt a different approach, using Arabidopsis thaliana, a model plant in plant biology whose genome is extremely well characterised and for which large collections of fully sequenced wild individuals are available.

Around 1,000 genotypes and several thousand pairs will be studied, testing the genome region by region to identify where genetic similarity influences interactions. “The grant will give us the resources to move from identifying candidate regions through to identifying and validating the biological mechanisms responsible,” says Germain Montazeaud. This will involve analysing the molecules produced by plants and using tools such as CRISPR-Cas9. Over the course of the five-year project, populations will also be allowed to evolve over several generations to determine whether the genes identified are favoured or eliminated by natural selection. The project will bring together a team with complementary expertise in molecular biology, population genomics and bioinformatics.

Could plants become new models for studying the evolution of social behaviour?

If such genes were identified, plants could become a new model for studying the evolution of social behaviour, showing that a form of genetic cooperation can arise even in organisms that have no nervous system and cannot move from place to place. “We already know that plants can reduce competition between one another by exploiting different resources — known as niche complementarity — or that one plant can improve the environment for another — known as ecological facilitation. PHYTOPOGON could reveal an additional mechanism: positive or negative interactions determined by the presence of particular gene variants in neighbouring plants,” explains Germain Montazeaud. Confirming the green beard theory in plants would make it possible to better predict the evolution, productivity and stability of plant communities. 

Better predicting the capacity to cooperate in crop mixtures

The project will also look for these mechanisms in crop species that are increasingly distant from Arabidopsis thaliana: first camelina, followed by Brassica rapa and Brassica oleracea, the two species from which oilseed rape originated. The aim is to reconstruct the evolutionary history of these genes and determine whether a mechanism discovered in Arabidopsis thaliana — a model plant but not a crop species — is also found in actual crops. If so, the gene could become a genetic marker that breeders could use to rethink the composition of varietal mixtures. These combinations of several varieties of the same species, grown side by side in the same field, are designed to optimise genetic diversity within the crop and limit the spread of disease. A pathogen adapted to one variety has greater difficulty overcoming the resistance of many different varieties at the same time. Breeders could instead select varieties that differ genetically across most of their genome but share the same version of this gene at the specific point in the genome where it promotes cooperation between them. 

The discovery behind the project

The idea dates back to Germain Montazeaud’s PhD, completed in 2019 at Institut Agro in Montpellier, where he was studying varietal mixtures and looking for regions of the genome in which genetic diversity protected against disease. Instead, he found the opposite: the combinations offering the greatest protection shared the same version of a gene at one specific point in the genome — “a counter-intuitive result that was difficult to explain”. He then chose to carry out post-doctoral research in the laboratory where the green beard effect in fire ants had been discovered, at the University of Lausanne, in order to apply concepts and tools from animal biology to plants. Since 2025, he has co-led the international PLANTCOM network, which focuses on the genetic basis of interactions between plants. Confirming such a discovery in plants would transform our understanding of social behaviour in plants, broaden the theory of kin selection and could inspire new approaches to more sustainable agriculture.

CV in brief

Career 

• Since 2024 - INRAE researcher in the GE²pop team, Institut AGAP, Montpellier 
• 2022-2024 - Marie Skłodowska-Curie Fellow, Department of Ecology and Evolution (DEE), University of Lausanne (Switzerland) 
• 2021 - Post-doctoral student at the University of Lausanne (Switzerland) 
• 2020 - Post-doctoral student, INRAE, Montpellier

Project leadership

• Since 2025 - Co-leader of PLANTCOM, an international research network on the genetic bases of plant-plant interactions

Degrees

• 2019 - Doctoral thesis – Revisiting cultivar mixtures in the light of ecological & evolutionary theories, Institut Agro, Montpellier
• 2016 - Master’s degree – Amélioration des plantes et génétique quantitative (Plant breeding and quantitative genetics), Institut Agro, Montpellier