The double-edged sword of plant defence
Rice plants defending themselves against chewing herbivores are actually more susceptible to insects that suck.
Many different animals feed on plants, including almost half of all known insect species. Some herbivores — like caterpillars for example — feed by chewing. Others, such as aphids and planthoppers, use syringe-like mouthparts to pierce plants and then feed on the fluids within.
To minimize the damage caused by these herbivores, plants activate specific defenses upon attack, including proteins that can inhibit the insect’s digestive enzymes. The inhibitors are effective against chewing herbivores but seem to have little or no effect on some insects that feed by the ‘pierce-and-suck’ method.
Investing in defense requires energy, and so plants attacked by herbivores actively slow their growth to meet this demand. Plants achieve this trade-off by changing the levels of different plant hormones. These hormones can control the expression of thousands of genes and have widespread effects throughout the plant. However, little is known about how prioritizing defense over growth in response to an attack by one herbivore affects the plant’s ability to defend itself against other herbivores.
Transcription factors are proteins that control which genes inside a cell are active or inactive. Ran Li and colleagues searched for a transcription factor in rice plants that was specifically triggered in response to an attack by the caterpillars of a moth called the rice striped stem borer. This search identified a protein called WRKY70 as a transcription factor that prioritizes defense over growth. WRKY70 achieves this by increasing the levels of a defensive plant hormone (called jasmonic acid) while reducing the levels of a growth hormone (called gibberellin). Further experiments show that the increase in jasmonic acid production is required to activate the enzyme inhibitors and for resistance against these caterpillars.
Li and colleagues then found that increased WRKY70 activity makes rice plants more susceptible to attack by a second herbivore, a piercing-sucking insect called the rice brown planthopper. Further experiments revealed that this is due to the reduced levels of gibberillin. These findings show that while prioritizing defense overgrowth is effective against some insect herbivores, it comes with a cost as it makes the plants more susceptible to attack by other herbivores. This trade-off has important implications for both the evolution of plant immunity, and efforts to exploit plant immunity to help protect crops from herbivore attack.
To find out more
Read the eLife research paper on which this story is based: “Prioritizing plant defence over growth through WRKY regulation facilitates infestation by non-target herbivores” (June 17, 2015).
eLife is an open-access journal for outstanding research in the life sciences and biomedicine.
This text was reused under a Creative Commons Attribution 4.0 International License.
