A Big Step Forward in Designing Drought-Tolerant Bioenergy Crops

The Science

Crassulacean acid metabolism (CAM) is a specialized mode of photosynthesis found in plants adapted to hot and arid conditions. CAM photosynthesis differs from the more common C3 and C4 photosynthesis types in that it inverts the day and night pattern of stomata opening to capture carbon dioxide (CO₂) at night and avoid water evaporation through stomata opening during the day. Researchers at the University of Nevada and Oak Ridge National Laboratory conducted metabolomics, proteomics, and transcriptomics analyses of the desert plant agave across a diel cycle to identify genes involved in the CAM photosynthesis process and its higher water-use efficiency.

The Impact

As the photosynthetic machinery of most bioenergy crops is adapted to temperate and humid environments, carbon fixation and, therefore, biomass accumulation are less efficient and require more water than CAM plants adapted to hot and dry conditions. For that reason, introducing CAM photosynthesis into bioenergy crops would enable them to grow in marginal environments, but the molecular and genetic basis of CAM photosynthesis are not well enough understood to do this. This research identified candidate genes responsible for several aspects of the CAM process that can be used to design bioenergy crops with increased water-use efficiency and tolerance to extreme environmental conditions.

Summary

A comparison of diel metabolic profiles of the CAM photosynthesis plant agave and the C3 photosynthesis plant Arabidopsis showed that metabolites involved in the redox reactions required for photosynthesis are found at different times of the day in each plant. Consistent with those results, transcription and protein profiling confirmed that the expression patterns of genes necessary for redox balance were shifted between agave and Arabidopsis through the day and night cycle. Furthermore, cell signaling genes in the guard cells that form the stomata, as well as CO2-sensing genes responsible for the closing of stomata and ion channels that participate in stomata opening, also showed the same opposite expression patterns between the two photosynthetic modes. This research provides strong evidence that bioengineering CAM in a C3 plant will require temporal reprogramming and identifies potential key targets for engineering this mode of photosynthesis in C3 plants, such as poplar and other selected bioenergy crops.

Principal Investigator(s)

Xiaohan Yang
Oak Ridge National Laboratory
[email protected]

John Cushman
University of Nevada
[email protected]

Funding

This work was supported by the Office of Biological and Environmental Research within the U.S. Department of Energy’s Office of Science award DE-SC0008834.

References

Abraham, P. E., H. Yin, A. M. Borland, D. Weighill, S. D. Lim, H. C. De Paoli, N. Engle, P.C. Jones, R. Agh, D. J. Weston, S. D. Wullschleger, T. Tschaplinski, D. Jacobson, J. C. Cushman, R. L. Hettich, G. A. Tuskan, and X. Yang. 2016. “Transcript, Protein, and Metabolite Temporal Dynamics in the CAM Plant Agave,” Nature Plants 2(16178), DOI:10.1038/nplants.2016.178.