Genomic Science Program
U.S. Department of Energy | Office of Science | Biological and Environmental Research Program

Engineering C4 Feedstock Crops for Improved Water Use Efficiency and Drought Avoidance


James Fischer1* (, Willian G. Viana2, Hector Torres Martinez2, José R. Dinneny2, Balasaheb Sonawane1, Andrew D. B. Leakey1, Ivan Baxter3


1University of Illinois Urbana-Champaign; 2Stanford University; 3Donald Danforth Plant Science Center



Bioenergy feedstocks need to be deployed on marginal soils with minimal inputs to be economically viable and have a low environmental impact. Currently, crop water supply is a key limitation to production. The yields of C4 bioenergy crops such as Sorghum bicolor have increased through breeding and improved agronomy. Still, the amount of biomass produced for a given amount of water use (water use efficiency, or WUE) remains unchanged. Therefore, the project aims to develop novel technologies and methodologies to redesign the bioenergy feedstock sorghum for optimal WUE. Within this broader context, this subproject is using Setaria viridis as a rapid cycling model for gene discovery. Researchers aim to develop and demonstrate novel methods and resources to accelerate both the production of genetic variants and phenotyping of WUE traits as part of reverse and forward genetics approaches to discover genes regulating stomatal patterning and water use efficiency.


To aid in biosystem design for improvement of WUE and drought avoidance researchers have recently investigated: (1) gene expression patterns during grass stomatal development; (2) impacts on internal leaf anatomy (i.e., intercellular air spaces) and gas exchange associated with variation in stomatal density; and (3) stacking greater leaf WUE with improved root systems.

Some orthologs of Arabidopsis genes implicated in stomatal development behave differently in sorghum, potentially a result of the co-option of genes into the construction of a more complex stomate or a result of the difference between the grass cell-file-system epidermis versus the Arabidopsis puzzle-piece epidermis. Candidate genes and promoters were identified for use in targeted expression of the transgene that drives lower stomatal density and greater WUE.

High-resolution microCT revealed stark differences between the airspaces below stomata on the adaxial versus abaxial leaf surfaces, with major potential implications for fluxes of carbon dioxide (CO2) and water. This may drive changes in mesophyll conductance that support greater WUE than if stomatal conductance alone was modified. Meanwhile, a survey of accessions varying in stomatal density from four sorghum races found that mesophyll conductance to CO2 is independent of stomatal density and positively influences intrinsic water use efficiency.

Root system size in bioenergy grasses is determined by initiation and growth of crown roots, a type of shoot-borne root. Researchers characterized a novel genetic locus, CROWN ROOT DEFECTIVE (CRD) that is necessary for crown root growth under well-watered conditions. Molecular characterization reveals that CRD encodes a WD-40 repeat protein that acts as a scaffold and physically interacts with proteins controlling hormone signaling. Physiological characterization suggests that CRD promotes crown root growth by suppressing ethylene biosynthesis.

Funding Information

This research was supported by the DOE Office of Science, BER Program, grant no. DE-SC0023160 and DE-SC0018277.