Grasses Fight Drought by Squelching Root Growth
Shoot-borne roots that normally start developing in grasses weeks after germination are suppressed under drought conditions.
Using fluorescent imaging technologies and direct observation of green foxtail roots excavated from soil, researchers discovered that root growth normally initiated from the crown (belowground shoot-root joint) is inhibited when water is scarce.
Drought tolerance is an important trait needed in bioenergy crops to enable their cultivation in marginal lands. As roots are the main conduit for water acquisition, understanding their biology is critical to discovering ways to improve bioenergy crops. The root system of potential bioenergy crops in the Poaceae family, such as switchgrass and sorghum, and the model grass Setaria viridis (green foxtail) is composed mostly by crown roots that emerge days or weeks after germination. However, little is known about their development under drought conditions. The discovery of a widespread mechanism of crown root suppression in grass species opens new avenues for improving bioenergy crop performance in dry environments.
A detailed study of root growth using traditional and new fluorescent imaging technologies in the model bioenergy crop Setaria showed that the crown (shoot-root node found belowground) senses the level of water conditions immediately surrounding the plant. At low soil humidity, root growth is arrested shortly after initiation, while root growth is rapidly resumed when water availability increases. Researchers from the Carnegie Institution for Science and international collaborators observed that drought-induced inhibition of root growth is also present in several other grasses, including the bioenergy crops sorghum and switchgrass and corn wild relatives, but not in highly domesticated corn lines. Furthermore, a corn mutant that lacks crown roots retains more water in the stem. These results suggest that grasses are adapted to inhibit root growth to preserve water and to induce crown root growth in response to precipitation to maximize water absorption in wet conditions. Genetic and transcriptomics analyses showed that oxidative-stress response genes may be involved in the process. The identification of the genes responsible for this phenomenon will be critical targets for engineering drought tolerance in bioenergy grasses.
Carnegie Institution for Science
This work was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research under award DE-SC0008769. Additional support was provided by the National Science Foundation.
Sebastian, J., M. Yee, W. Viana, R. Rellán-Álvarez, M. Feldman, H. Priest, C. Trontin, T. Lee, H. Jiang, I. Baxter, T. Mockler, F. Hochholdinger, T. Brutnell, and J. Dinneny. 2016. “Grasses Suppress Shoot-Borne Roots to Conserve Water During Drought,” Proceedings of the National Academy of Sciences (USA) 113(31), 8861-66. DOI: 10.1073/pnas.1604021113.