Plant defense mechanism can optimize agriculture – 10/02/2024 – Fundamental Science

Among all biological relationships, few are as recurrent and ecologically significant as the interaction between plants and insects, which puts two empires face to face: plants, which represent more than 80% of all terrestrial biomass, and insects, the most diverse group of organisms on the planet, with more than a million different species described.

When insects act as pollination agents in exchange for nectar, or plants offer them shelter in exchange for defense against large predators, the interaction between these groups can be mutually beneficial. However, the most common form of contact between the two generates negative consequences for the plant: it is called herbivory.

More than half of the known insect species have their main nutritional source in plant tissues, and all this plant-based nutrition can slow down their development or even lead to their death. The relationship between plants and herbivorous insects is often described as an evolutionary “arms race”, in which plants are constantly developing defense barriers against herbivorous insects, while the insects never stop searching for mechanisms to optimize the exploitation of plant tissues.

Minimizing the attack of herbivorous insects is one of the greatest challenges in ensuring food security on the planet. It is estimated that the damage caused by these insects reduces the productivity of our main crops, such as soybeans, rice and corn, by up to 40%. Every year, tens of billions of dollars are spent on pesticides, many of which are toxic to humans and the ecosystem. This situation has become even more complex due to global warming, which increases the voracity of insects and reduces the defense capacity of plants.

However, a walk through a vegetable garden or any other plantation can reveal that the number of insect species that can actually attack a plant species is impressively small compared to the total number of herbivorous insects in the world. The tomato, for example, is one of the plants whose cultivation is most risky due to attack by insects. Of the approximately 500,000 species of herbivorous insects that exist, only a few hundred cause significant problems for tomato plants.

If we leave the agricultural environment towards a more natural ecosystem (such as a forest or the savannah), we will notice that, despite the destructive potential of herbivorous insects, the plants generally appear healthy. In other words, in the plant kingdom, susceptibility to attack by insects is the exception rather than the rule.

There are several explanations for this fact, including the simple geographic isolation between a plant species and a herbivorous insect. However, the finding that pests that are highly destructive to a plant do not cause damage to another that is neighboring it confirms the existence of effective defense mechanisms in plants, such as hairs on the surface of the leaves, poisons produced to intoxicate insects or proteins that make it difficult the digestion of plant material.

Only an insect capable of breaking through all these defenses will be able to use the plant as a host. When a predator does not overcome a plant’s defense mechanisms and therefore does not use it as a food source, we say that “non-host resistance” (NHR) occurs.

The RNH provides a curious explanation for why so few insect species can interact with a plant species: their defense mechanisms are so effective against pest attacks that few insects can overcome them. From an evolutionary perspective, RNH forces most insects to specialize on a specific group of host plants, reducing the niche of species they are able to feed on.

My laboratory is dedicated to research on NHR, seeking to isolate defense mechanisms associated with this phenomenon and study how they act in different species of herbivorous insects. From plants with modifications in the immune system, we have already identified some groups of plant signaling molecules that are associated with RNH.

In an article recently published in the scientific journal Journal of Experimental Botany, we detail what is known about the functioning of the RNH and how it is one of the ecological parameters that delimit the extent of interactions between plants and herbivorous insects on our planet. The RNH represents a phenomenal and relatively unexplored opportunity to produce plant cultivars that are more resilient to attack by pests.

If, for example, we identify how a grass defends itself against a tomato predator insect, we can transfer this resistance mechanism to the tomato, making its cultivation much safer, both economically and ecologically. RNH can be a key player in ensuring global food security, transforming agriculture and ensuring a more sustainable future.

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Marcelo Lattarulo Campos is a professor of botany at the UFMT Biosciences Institute. Studies on RNH in his laboratory are financed by the Serrapilheira Institute.

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