What's the cost of mounting a defense to insect attack? For plants, it's a tradeoff with growth and reproduction. Typically, plants switch on their defense system to ward off attacks as they occur. As part of this defensive response, the plant makes a toxin to help ward off the attacker. When the threat passes, the plants use their available energy and resources to grow and reproduce. Scientists engineered mouse-eared cress, a common weed, so that it is always mounting a defensive response—even when it is not under attack from insects. The team showed that the modified plant uses the bulk of its energy and resources for defense and making this toxin, resulting in poor growth and few seeds.
This fundamental study is helping scientists understand the metabolic tradeoffs resulting from growth-defense decisions made by plants. Knowing what affects a plant's growth and seed production can lead to new strategies to help increase crop yields. As well, knowing how a plant defends itself from an insect attack can provide new approaches to reduce the use of pesticides.
Regardless of what crops they are growing, farmers want to increase the yields and reduce the use of costly pesticides. Using less of such chemicals means the plants may have to work harder to defend against insects and other herbivores. Researchers delved into the genetics of the defense systems used by a common plant, mouse-ear cress, to better understand the tradeoff between defense and growth. They selected this plant because when under attack, it releases a toxin, an obvious defense system. Through genetic modification, they created a form of mouse-ear cress that was always mounting its defensive response. They found that this always-on defense system notably compromises growth and reproduction in the plant (flowering and seed production). The team's findings support the long-held paradigm known as the growth-defense tradeoff, which is that plants prioritize how they use their available resources depending on their immediate needs.
Gregg A. Howe
Michigan State University
This work was primarily funded by the Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of Science, Department of Energy. Construction of mutant lines was supported by National Institutes of Health. K.S. was supported in part by the Japan Society for Promotion of Science Research Fellowship for Young Scientists Award. The authors also acknowledge support from the Michigan AgBioResearch Project and the Discretionary Funding Initiative from Michigan State University.
Q. Gao, Y. Yoshida, I.T. Major, K. Wang, K. Sugimoto, G. Kapali, N.E. Havko, C. Benning, and G.A. Howe, "JAZ repressors of metabolic defense promote growth and reproductive fitness in Arabidopsis." Proceedings of the National Academy of Sciences USA 115(45), E10768 (2018). [DOI: 10.1073/pnas.1811828115]
Michigan State University press release: Overspending on Defense Arsenal Bankrupts a Plant's Economy