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

Discovering Transcriptional Regulators of Photosynthesis in Energy Sorghum to Improve Productivity

Authors:

Matthew Brooks4* (matthew.d.brooks@usda.gov), Elena Pelech1, Atinder Singh2, Kithmee De Silva3, Antony Maodzeka2, Steve Long1,3,5, Laurie Leonelli2

Institutions:

1Carl R. Woese Institute for Genomic Biology, University of Illinois Urbana-Champaign; 2Department of Agricultural and Biological Engineering, University of Illinois Urbana-Champaign; 3Department of Plant Biology, University of Illinois Urbana-Champaign; 4Global Change and Photosynthesis Research Unit, USDA-ARS; 5Department of Crop Sciences, University of Illinois Urbana-Champaign

URLs:

Goals

This research aims to identify and investigate the transcription factors involved in the regulation of photosynthesis in energy sorghum. The major goal of this project is to model and validate gene regulatory networks and integrate with physiological data to reveal transcription factors that can alleviate the loss of photosynthetic efficiency in lower canopy leaves. This information will allow ranking of transcription factors by importance and thus, will guide future design strategies for developing energy sorghum cultivars with improved photosynthetic light-use efficiency and overall productivity.

Abstract

C4 grasses such as energy sorghum (Sorghum bicolor) have great potential for both carbon sequestration and as feedstocks for biofuels and building materials. However, in contrast to what is typically observed for other plants, sorghum belongs to a clade of C4 species that has undergone a maladaptive loss of photosynthetic efficiency in self-shaded leaves within the canopy. Current models predict that this loss results in a 15 to 20% reduction in potential productivity (Pignon et al. 2017). Specifically, most plants have evolved to dynamically tune their photosynthetic machinery by shifting the stoichiometry of proteins involved in the light reactions of photosynthesis to maintain a high maximum absolute quantum efficiency of carbon dioxide (CO2) assimilation (ΦCO2,max) in the shade. Work has shown that the lower self-shaded leaves from C4 bioenergy crops (bioenergy sorghum, Miscanthus, and maize) do not retain a high ΦCO2,max compared to their upper sun-exposed leaves; this change is due to the light environment rather than leaf age (Collison et al. 2020; Pignon et al. 2017). Variation in the severity of this ΦCO2,max loss between sorghum cultivars suggests that this maladaptive trait may be the result of difference in the expression of one or more genes (Jaikumar et al. 2021). This is supported by recent greenhouse experiments where researchers showed that the phenotype is reversible by moving plants from shaded to light environments. The team hypothesizes that genes influencing ΦCO2,max will have expression patterns that correspond to measurable changes in photosynthetic traits and that researchers will be able to identify these genes by comparing changes in expression in response to the light environment across energy sorghum cultivars and canopy positions.

Therefore, the team will have collected gene expression and physiological data on photosynthetic traits such as ΦCO2,max across light conditions from different sorghum cultivars in the field and greenhouse. Since transcription factors (TFs) are key regulators of gene expression in response to environmental stimuli such as changes in light intensity and quality, the project expects that TF expression is important to the maladaptive loss of photosynthetic efficiency. To identify key TFs, researchers are building gene regulatory networks that integrate the gene expression and photosynthetic trait data. The project will improve the accuracy of these networks by including TF gene targets identified using a new in planta method. Identifying the cause of photosynthetic inefficiency in shaded energy sorghum canopies and engineering solutions to restore the 15 to 20% loss in productivity and enhance yield will improve the overall potential of this bioenergy crop to meet the growing needs for energy security.

References

Collison, R. F., et al. 2020. “Light, Not Age, Underlies the Maladaptation of Maize and Miscanthus Photosynthesis to Self-Shading,” Frontiers in Plant Science 11, 783. DOI:10.3389/fpls.2020.00783.

Jaikumar, N. S., et al. 2021. “Can Improved Canopy Light Transmission Ameliorate Loss of Photosynthetic Efficiency in the Shade? An Investigation of Natural Variation in Sorghum bicolor,” Journal of Experimental Botany 72(13), 4965–80. DOI:10.1093/jxb/erab176.

Pignon, C. P., et al. 2017. “Loss of Photosynthetic Efficiency in the Shade. An Achilles Heel for the Dense Modern Stands of Our Most Productive C4 Crops?” Journal of Experimental Botany 68(2), 335–45. DOI:10.1093/jxb/erw456.

Funding Information

This research is supported by the U.S. DOE Office of Science, BER program, grant no. DE-SC0023107. This program is supported by the U. S. DOE, Office of Science, through BER’s GSP under FWP ERKP123.