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

Leveraging Leaf Structure and Biochemistry to Enhance Water Use Efficiency in Sorghum

Authors:

Haley Schrader1* (haley.schrader@wsu.edu), Erik Myers2, Hui Jiang3, Britney Millman3, Daniel Voytas2, Asaph Cousins1, Ivan Baxter3

Institutions:

1Washington State University; 2University of Minnesota; 3Donald Danforth Plant Science Center

URLs:

Goals

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; WUE) remains unchanged. Therefore, this 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. The team’s goal is to devise novel methods and develop resources to create genetic variations and streamline the phenotyping of WUE traits. These advancements are crucial for their application in forward genetics approaches aimed at identifying genes that regulate the efficiency of the carbon-concentrating mechanism (CCM) and WUE.

Abstract

At the whole-plant scale, water use efficiency (WUE) is defined as biomass production per unit of water loss through transpiration. Plant WUE is largely determined by leaf-level “intrinsic” WUE, which is defined as the ratio of photosynthetic carbon gain (Anet) to stomatal conductance to water vapor (gs). The intrinsic WUE in C4 plants such as Sorghum is generally high because they use a carbon-concentrating mechanism (CCM) to increase Anet while maintaining low gs. However, under drought conditions Anet can be limited by insufficient supply of carbon dioxide (CO2) to drive the CCM. The focus of the research presented here is to enhance intrinsic WUE in Sorghum by (1) increasing the conductance of CO2 within the leaf to overcome reduced gs and (2) to enhance the catalytic efficiency of the first committed reaction of the CCM catalyzed by phosphoenolpyruvate carboxylase (PEPC).

The conductance of CO2 within the leaf’s mesophyll is partially determined by cell wall structural polymers that influence wall thickness and porosity. The group has demonstrated changes in cell wall mixed-linkage glucans and ferulic/coumaric acids influence leaf CO2 and H2O conductance that led to an increase in whole plant WUE. This research team is also using a forward genetic screen to identify other key genes that influence traits related to the internal conductance of CO2 and leaf intrinsic WUE.

Additionally, researchers have determined that variation in the affinity of PEPC for bicarbonate (HCO3; KHCO3) across several C4 species is sufficient to increase modelled Anet under low gs that occurs during drought. Researchers have further demonstrated using a heterologous Escherichia coli expression system that they can engineer enhanced in vitro PEPC kinetic properties with specific modifications to key amino acid residues. These modifications are also predicted through models of C4 photosynthesis to increase photosynthesis under low gs and enhance WUE. To translate these findings into plant systems, the team is using prime editors to create heritable edits of these key amino acid residues. Researchers are currently phenotyping plants engineered with these modified PEPCs to determine the impact on intrinsic and whole-plant WUE.

Funding Information

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