A Systems Understanding of Nitrogen-Fixation on the Aerial Roots of Sorghum
Authors:
Saddie Vela1, Emily Wolf1, Jennifer Wilker2, Megan Kelly1, Saptarshi Pyne2, Sushmita Roy2, Jean-Michel Ané2, and Wilfred Vermerris1* (wev@ufl.edu)
Institutions:
1University of Florida; and 2University of Wisconsin–Madison
URLs:
Goals
This project aims to understand the molecular and cellular networks controlling biological nitrogen fixation in sorghum aerial roots using a combination of genetics, synthetic bacterial communities, and systems biology.
Abstract
Biological nitrogen fixation (BNF) by crop plants via microbial symbiosis is an effective approach to lowering the economic and environmental costs of crop production by decreasing fertilizer dependence. BNF is commonly associated with legumes, but cereals have been reported to be able to support nitrogen-fixing bacteria in the mucilage of their aerial roots (adventitious nodal roots), such as indigenous landraces of maize (Zea mays L.) in Oaxaca, Mexico (Van Deynze et al. 2018). Sorghum (Sorghum bicolor (L.) Moench) is an attractive bioenergy crop due to its ability to produce high biomass yields with minimal inputs and to withstand biotic and abiotic stresses. Some sorghum accessions can host nitrogen-fixing bacteria in the mucilage produced by their aerial roots, and this project is investigating the mechanisms enabling the symbiotic interactions with nitrogen-fixing microbes. Since this interaction relies on the presence of aerial roots, researchers have performed a genome-wide association study (GWAS) of two panels of genetically diverse sorghum genotypes, the sorghum minicore (Upadhyaya et al. 2009), a collection of landraces, and the sorghum association panel (SAP; Casa et al. 2008), a collection of sorghum genotypes representing all major cultivated races and important U.S. breeding lines and their progenitors. Traits of interest include the number of nodes producing aerial roots, the total number of aerial roots, aerial root length, and aerial root diameter. Since the traits supporting efficient BNF are hypothesized to be under genetic control but influenced by the environment, the team has also analyzed the effect of the nitrogen fertilization level and location (Florida vs. Wisconsin) on these traits. The proportion of genotypes forming aerial roots was substantially greater in the minicore than in the SAP, suggesting the presence of aerial roots has been under negative selection in modern breeding programs. The GWAS resulted in several candidate loci associated with the number of nodes producing aerial roots consistently in both locations. The genetic analysis of segregating breeding populations derived from crosses between commercial bioenergy sorghums and landraces that form aerial roots will be used to validate these loci. In addition, backcross populations with inbred line RTx430 will be the basis for future transgenic validation experiments with an improved sorghum leaf-whorl transformation system (Silva et al. 2020).
References
Casa, A. M., et al. 2008. “Community Resources and Strategies for Association Mapping in Sorghum,” Crop Science 48, 30–40.
Silva, T., et al. 2020. “Use of Sorghum bicolor Leaf Whorl Explants to Expedite Regeneration and Increase Transformation Throughput,” Plant Cell, Tissue and Organ Culture 141, 242–55.
Upadhyaya, H. D., et al. 2009. “Developing a Mini Core Collection of Sorghum for Diversified Utilization of Germplasm,” Crop Science 49, 1769–80.
Van Deynze, A., et al. 2018. “Nitrogen Fixation in a Landrace of Maize Is Supported by a Mucilage-Associated Diazotrophic Microbiota,” PLoS Biology 16, e2006352.
Funding Information
The authors gratefully acknowledge funding from the U.S. Department of Energy Biological and Environmental Research (BER) Program grant no. DE-SC0021052.