Location: Plant, Soil and Nutrition ResearchTitle: Genotypic recognition and spatial responses by rice roots Author
Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/2012
Publication Date: 1/4/2013
Citation: Suqin, F., Clark, R., Zheng, Y., Iyer-Pascuzzi, A.S., Weitz, J., Kochian, L.V., Edelsbrunner, H., Liao, H., Benfey, P. 2013. Genotypic recognition and spatial responses by rice roots. Proceedings of the National Academy of Sciences. 110(7):2670-2675. Interpretive Summary: There is a growing realization by agricultural researchers about the importance of root systems to crop traits such as nutrient and water acquisition and utilization, and plant-plant interactions in the field. It has been shown in many studies that when two plants that are different plant species are grown close to each other, they can influence the growth of the other plant. It has been suggested there is a genetic and biochemical component to this interaction. In this study, two rice plants that were either the same cultivar or two different cultivars were grown near each other in a transparent gel system. The root systems were imaged and the images reconstructed to depict the entire root system architecture in 3 dimensions. When two rice plants of the same cultivar were grown next to each other, the root systems overlapped to a much higher degree than for root systems from two different rice cultivars. Further experimentation showed that the root interactions did not involve the shoots of each plant, suggesting the roots were communicating with each other. Subsequent work showed this was the case and the interaction appears to be due to interactions through the root tips of roots growing in close proximity. The study also looked at root interactions with physical objects and this appears to involve root recognition of the physical obstruction through physical contact. These findings suggest roots use two different forms of communication: root-root recognition, possibly through the release of chemical compounds from the root tips, and recognition of physical objects in the soil via physical contact with the root. These findings indicate the root tips may be local sensors of the soil environment, which then influences changes in global root architecture. This information will be useful for future studies aimed at designing crop species with root systems that more efficiently grow in the soil, acquire nutrients, and avoid stressful interactions.
Technical Abstract: Root system growth and development is highly plastic and is influenced by the surrounding environment. Roots frequently grow in heterogeneous environments that include competition from neighboring plants and physical impediments in the rhizosphere. To investigate how planting density and physical objects affect root system growth, we grew rice in a transparent gel system in close proximity with another plant or a physical object. Root systems were imaged and reconstructed in three dimensions. Root-root intersection strength was calculated using quantitative metrics that characterize the extent to which the reconstructed root systems overlap each other. Surprisingly, we found the overlap of root systems of the same genotype was significantly higher than that of root systems of different genotypes. Root systems of the same genotype tended to grow toward each other while those of different genotypes appeared to avoid each other. Shoot separation experiments excluded the possibility of aerial interactions, suggesting root communication. Staggered plantings indicated that interactions likely occur at root tips in close proximity. Recognition of obstacles also occurred through root tips, but through physical contact in a size-dependent manner. These results indicate that root systems use two different forms of communication to recognize objects and alter root architecture: root-root recognition, possibly mediated through root exudates, and root-object recognition mediated by physical contact at the root tips. This suggests that root tips act as local sensors that integrate rhizosphere information into global root architectural changes.