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Battening down the hatches: priming plant defense

Press/Media: Research

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It is widely accepted that achieving agricultural sustainability means reducing our reliance on synthetic agrochemicals. One major group of agrochemicals are pesticides, including the insecticides and fungicides that protect crop plants against pests and diseases. Pests and diseases aren’t going to go away, so reducing pesticide usage means that alternative crop protection approaches are needed. EU Directive 2009/128/EC (Sustainable Use of Pesticides) recommends the use of integrated pest and disease management (IPM) – the use of multiple approaches that together provide sufficient protection.

Our contribution has been to identify ways in which we might enhance plants’ own natural defence mechanisms. Plants have a wide array of structural and chemical defences that they can employ to fight of enemies. Many of these are inducible, meaning that they are only activated in response to attack. The reason for this is that defence comes at a cost, and inducible responses balance these costs against the benefits of defence. For crop plants, these costs can often translate into reduced yields. Spraying with compounds that switch on inducible defences, such as the plant hormones jasmonic acid (JA) and salicylic acid (SA), can make plants more resistant, but this approach also risks unwanted growth reductions.

Fortunately, evolution has produced another way of regulating inducible defences that we can take advantage of: the phenomenon we refer to as ‘priming’. When we ourselves get infected with something like a virus, our immune system generates antibodies to quickly fight it off, but it also produces memory cells that can respond to the same infection many months, or even years, in the future, with a more rapid and effective immune response. This is the basis of the familiar concept of vaccination. Whilst plants don’t make antibodies, they are nevertheless able to alter future patterns of defence activation in response to previous infection by disease or feeding by herbivorous insects. Thus, priming results in a faster and stronger activation of future inducible defence responses.

If we can find ways to prime defences in crop plants, we might be able to improve pest and disease resistance with minimal impacts on yield. One way to do this is through seed treatments. We found that treating seed with the defence hormone JA, provides long-term enhanced resistance against herbivory and some fungal diseases, without affecting growth and development. We were able to patent this discovery, and the approach has since been successfully commercialised. The same approach can also be used to prime defences against other forms of biotic and abiotic stress.

How and why seed treatments provide long-term defence priming might perhaps be explained by the phenomenon of transgenerational immune priming, which my lab has also been involved in elucidating. After our success with the seed treatment, we wondered “What if seeds were exposed to hormones like JA during the course of their development on the parent plant?” We tested this by infecting plants with bacteria or exposing them to herbivores, and then examined defence phenotypes in their offspring. Remarkably, we saw that priming responses established in the parent were passed on to the offspring; something we refer to as transgenerational immune priming.

The evidence we have at present suggests that the mechanism for this heritable stress memory is epigenetic. That is, the genes that control priming are chemically-tagged to alter their activity. These epigenetic modifications don’t involve changes in the DNA sequence, and are reversible, allowing rapid, flexible responses to environmental stress. Understanding the nature of these epigenetic changes may provide another way to exploit priming for crop protection. Introducing the right epigenetic marks onto genes in elite crop varieties may enable priming of defence without altering their genetic make-up. Given the difficulty of introducing new chemical and biological methods of crop protection, which require time-consuming and costly regulatory approval before they can be brought to market, this could prove an especially attractive option in the future.

Period12/12/2016

It is widely accepted that achieving agricultural sustainability means reducing our reliance on synthetic agrochemicals. One major group of agrochemicals are pesticides, including the insecticides and fungicides that protect crop plants against pests and diseases. Pests and diseases aren’t going to go away, so reducing pesticide usage means that alternative crop protection approaches are needed. EU Directive 2009/128/EC (Sustainable Use of Pesticides) recommends the use of integrated pest and disease management (IPM) – the use of multiple approaches that together provide sufficient protection.

Our contribution has been to identify ways in which we might enhance plants’ own natural defence mechanisms. Plants have a wide array of structural and chemical defences that they can employ to fight of enemies. Many of these are inducible, meaning that they are only activated in response to attack. The reason for this is that defence comes at a cost, and inducible responses balance these costs against the benefits of defence. For crop plants, these costs can often translate into reduced yields. Spraying with compounds that switch on inducible defences, such as the plant hormones jasmonic acid (JA) and salicylic acid (SA), can make plants more resistant, but this approach also risks unwanted growth reductions.

Fortunately, evolution has produced another way of regulating inducible defences that we can take advantage of: the phenomenon we refer to as ‘priming’. When we ourselves get infected with something like a virus, our immune system generates antibodies to quickly fight it off, but it also produces memory cells that can respond to the same infection many months, or even years, in the future, with a more rapid and effective immune response. This is the basis of the familiar concept of vaccination. Whilst plants don’t make antibodies, they are nevertheless able to alter future patterns of defence activation in response to previous infection by disease or feeding by herbivorous insects. Thus, priming results in a faster and stronger activation of future inducible defence responses.

If we can find ways to prime defences in crop plants, we might be able to improve pest and disease resistance with minimal impacts on yield. One way to do this is through seed treatments. We found that treating seed with the defence hormone JA, provides long-term enhanced resistance against herbivory and some fungal diseases, without affecting growth and development. We were able to patent this discovery, and the approach has since been successfully commercialised. The same approach can also be used to prime defences against other forms of biotic and abiotic stress.

How and why seed treatments provide long-term defence priming might perhaps be explained by the phenomenon of transgenerational immune priming, which my lab has also been involved in elucidating. After our success with the seed treatment, we wondered “What if seeds were exposed to hormones like JA during the course of their development on the parent plant?” We tested this by infecting plants with bacteria or exposing them to herbivores, and then examined defence phenotypes in their offspring. Remarkably, we saw that priming responses established in the parent were passed on to the offspring; something we refer to as transgenerational immune priming.

The evidence we have at present suggests that the mechanism for this heritable stress memory is epigenetic. That is, the genes that control priming are chemically-tagged to alter their activity. These epigenetic modifications don’t involve changes in the DNA sequence, and are reversible, allowing rapid, flexible responses to environmental stress. Understanding the nature of these epigenetic changes may provide another way to exploit priming for crop protection. Introducing the right epigenetic marks onto genes in elite crop varieties may enable priming of defence without altering their genetic make-up. Given the difficulty of introducing new chemical and biological methods of crop protection, which require time-consuming and costly regulatory approval before they can be brought to market, this could prove an especially attractive option in the future.

References

TitleBattening down the hatches: priming plant defense
Degree of recognitionInternational
Media name/outletWeb
Media typeWeb
Duration/Length/SizeGlobal Plant Council blog
Date12/12/16
Producer/AuthorMike Roberts
PersonsMike Roberts