- Also called:
- matching-gene coevolution
- Related Topics:
- coevolution
gene-for-gene coevolution
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What is gene-for-gene coevolution?
Gene-for-gene coevolution is a reciprocal evolutionary change where one species develops a gene that affects its relationship with another species, prompting the other to evolve a counteracting gene. This coevolution has been observed in plants and their parasites, such as fungi, nematodes, bacteria, viruses, and some insects.
The process starts when a parasite encounters a new host plant. Plants with a mutated resistance gene can detect substances emitted by the parasite, allowing them to prevent invasion. The parasite can then evolve a mutation to avoid detection, leading to a continuous genetic interaction between host and parasite as they accumulate matching genes. An example of this is seen in wild flax and flax rust in Australia, where the number and frequency of resistance genes fluctuate over time as coevolution occurs.
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How does gene-for-gene coevolution occur between plants and their pathogens?
Gene-for-gene coevolution is a reciprocal evolutionary change where one species' gene affects its relationship with another species, prompting the other to evolve a counter-acting gene. This coevolution starts when a parasite meets a new plant host. Plants with a mutated resistance gene can detect substances from the parasite's avirulence gene and prevent invasion. This resistance gene spreads in the plant population, but parasites can mutate to avoid detection, leading to a "genetic Ping-Pong match" where both species accumulate matching genes and coevolve. An example is wild flax and flax rust, where the number and frequency of resistance genes fluctuate over time as coevolution continues.
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What is a resistance gene in a plant?
In gene-for-gene coevolution, a resistance gene in a plant allows it to detect a substance emitted by a parasite, which is encoded by an avirulence gene. This detection alerts the host plant to prevent the parasite from invading. Plants with the resistance gene have an advantage, enabling them to survive, reproduce, and pass on their genotype to future generations.
Resistance genes are introduced into plants to help them fight off pathogens. Plants can have either total resistance (immunity) or partial resistance (tolerance) to a pathogen. Vertical resistance provides a high degree of resistance to a single race of a pathogen and is controlled by a few plant genes. Horizontal resistance protects plants against several strains of a pathogen, involving many genes.
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How do avirulence genes in pathogens interact with plant resistance genes?
In gene-for-gene coevolution, a plant host uses a resistance gene to detect a substance emitted by a parasite, which is encoded by an avirulence gene. If the host detects the parasite, it prevents invasion. The resistance gene spreads among plants, allowing them to survive and pass on their genotype.
To counter this, a mutation may arise in the parasite's avirulence gene, altering the substance, so the host can no longer resist it. The mutant gene spreads in the parasite population through natural selection. A "genetic Ping-Pong match" ensues as the host develops another mutation to detect the parasite, and the parasite responds with a genetic alteration to avoid detection. The host and parasite populations coevolve through the accumulation of these matching genes.
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Why is gene-for-gene coevolution important in agriculture?
Gene-for-gene coevolution is vital in agriculture because it introduces new resistance genes into plants across large areas, increasing their resistance to parasites and pathogens. This coevolution is a reciprocal evolutionary change where, for every gene a species develops to affect a relationship, the interacting species develops a counter-gene.
The process starts when a parasite encounters a new host plant. Plants with a mutated resistance gene can detect substances emitted by the parasite, preventing invasion. This resistance gene spreads, giving these plants an advantage. Parasites can then evolve to circumvent this by altering the recognized gene product, leading to a continuous coevolutionary cycle maintained in agriculture through the introduction of new resistance genes.
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How does gene-for-gene coevolution affect the diversity of plant and pathogen populations?
Gene-for-gene coevolution is a reciprocal evolutionary change where one species develops a gene to counter the effect of a gene in another interacting species. This dynamic has been observed between plants and their parasites, such as fungi, nematodes, bacteria, viruses, and insects.
This coevolution begins when a parasite encounters a new plant host. Plants with a mutated resistance gene can detect substances emitted by the parasite, preventing invasion. This resistance gene spreads, but parasites can then mutate to avoid detection, leading to a continuous genetic interaction between host and parasite populations. The number and frequency of these genes fluctuate over time, and can be lost through genetic drift in small populations. New genes arise through mutation or gene flow from other populations.
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gene-for-gene coevolution, a specific form of reciprocal evolutionary change based on the idea that, if one member of a coevolving relationship has a gene that affects the relationship, the other member has a gene to counter this effect. These genes evolve reciprocally and provide the genetic basis for certain types of coevolution. This relationship has been demonstrated between plants and a number of their parasites, including rust fungi, nematodes, bacteria, viruses, and one insect species. Its principles also form the basis of many plant-breeding programs designed to increase resistance against pathogens.
The process of gene-for-gene coevolution begins when a parasite population encounters a new plant host. Most host individuals will not be able to detect the presence of the parasite. Certain host individuals, however, may have a mutated gene, dubbed the resistance gene in this scenario, that allows them to detect a substance the parasite emits, encoded by a so-called avirulence gene. After being alerted to the threat of the parasite, the host responds to prevent the parasite from invading. The resistance gene will confer an advantage to plants that carry it, allowing individuals to survive and pass on their genotype to future generations. Individuals that do not possess this gene will not be able to resist invasion by the parasite and will die, unable to pass on their genotype. Thus, the new resistance gene will spread through the plant population. At this point the parasite might seem to be outwitted, but actually it may be able to circumvent this genetic evasion by the host with a genetic trick of its own. If a mutation arises in the gene that codes for the product that the host recognizes, the gene product will be altered and the host will no longer be able to resist the parasite. The spread of this mutant gene in the parasite population will be favoured by natural selection. A genetic Ping-Pong match between the two species can then ensue, as the host develops another mutation in any gene that allows it to detect the parasite, and the parasite responds to this defensive maneuver with a genetic alteration to avoid detection. The host and parasite populations therefore coevolve by the accumulation of these matching genes.
In agriculture, gene-for-gene relationships are maintained by introducing new resistance genes into all plants that cover a large area. In natural populations, each new resistance gene appears as a mutant in a single individual and then spreads by natural selection throughout the population in subsequent generations. Demonstrating a gene-for-gene relationship in natural populations is a difficult and time-consuming process because it demands detailed genetic and ecological studies of the plants and their pathogens that take many years.
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The best-studied example is that of wild flax (Linum marginale) and flax rust (Melampsora lini) in Australia. Local populations of flax plants and flax rust harbour multiple matching genes for resistance and avirulence. The number of genes and their frequency within local populations fluctuate greatly over time as coevolution continues. In small populations, the resistance genes can be lost by chance alone through the process of genetic drift. New genes in the host and parasite populations can appear through either mutation or the influx of genes from other populations. Consequently, the long-term dynamics of the gene-for-gene coevolution between flax and flax rust depend on the rate at which new genes appear within local populations of the parasite and host, the intensity with which natural selection acts on these genes (which, in turn, depends on the virulence of the particular parasite genotype), the population sizes of both host and parasite, and the rate that genes are transferred among populations.
Not all interactions between plants and parasites coevolve in a gene-for-gene manner. Resistance in a plant host is often determined by many genes rather than by a single gene. Examples of gene-for-gene coevolution, however, are slowly accumulating, and these are providing powerful tools for breeding crop plants that are resistant to pathogens and parasites. As other forms of coevolution are studied in natural populations, the results will help determine still other ways of selecting for more durable resistance in crop plants. Such studies, however, require that intact biological communities be preserved as precious natural laboratories for understanding the coevolutionary process.