Switchgrass community gardens help distinguish genetic bases of fitness traits from climactic influence.
To better understand the genetic basis of local adaptation, researchers established community gardens of switchgrass plants in 10 different field sites on a north-south gradient across the United States. Hundreds of the switchgrass plants in these gardens are clonally propagated crosses between southern lowland and northern upland ecotypes. Early results from these large-scale field tests conducted over two years reveal fewer tradeoffs in plant fitness and adaptation than expected.
The perennial grass switchgrass (Panicum virgatum) is a candidate bioenergy feedstock, with deep roots that allow it to access nutrients easily from a variety of soils and a higher tolerance for extreme water conditions. The U.S. Department of Energy (DOE) is interested in finding ways of increasing the plant’s biomass yield to develop sustainable biofuels. By field-testing the adaptability of switchgrass hybrids in a wide range of environmental conditions, researchers hope to eventually develop a “generalist” switchgrass that would thrive and produce high levels of biomass in various regions.
In plant nurseries, the plants often have tags that note their best growing conditions such as full sun, infrequent watering, and even favorable growing regions within the country. These notes highlight local adaptation, or how a plant has adapted to thrive within a specific set of environmental conditions. In the Proceedings of the National Academy of Sciences, a multi-institution team led by Tom Juenger at the University of Texas at Austin, and including researchers at the Great Lakes Bioenergy Research Center and the U.S. Department of Energy Joint Genome Institute (JGI), a DOE Office of Science User Facility, conducted a large-scale field experiment to uncover the genetic basis of local adaptation in switchgrass.
Collaborating with a community of switchgrass researchers, Juenger’s team developed switchgrass hybrids, more than 400 of which were then clonally propagated and sent to 10 field sites in multiple states, representing 17 degrees of latitude within the country. Having the same plants growing at these community gardens – a method previously applied to poplar, one of the JGI’s Flagship Plant Genomes – allowed researchers to consider how the plant’s genes interact with the environment, and look at the genes involved in specific fitness traits such as biomass production and flowering time with the aid of a method called quantitative trait locus (QTL) mapping. Samples were regularly collected at the sites over two full years, with sequencing and analysis assistance through the JGI’s Community Science Program. The switchgrass genomes are available on the JGI’s plant portal Phytozome.
Among the team’s findings: location determined when the switchgrass plants flowered and emerged in spring (green up); gardens further south flowered earlier than those in the north. Additionally, they found that contrary to expectations, they had fewer tradeoffs in the genetic contributions to local adaptation across the geographic range of the study. For example, variants of genes from the lowland ecotype increased biomass production at many of the field sites, or were neutral compared to the variants of genes from the northern upland ecotype. These results are helping them sort out the traits and underlying genes to help develop a switchgrass cultivar with high biomass production in multiple planting zones.
Ramana Madupu, Ph.D.
Biological Systems Sciences Division
Office of Biological and Environmental Research
Office of Science
US Department of Energy
The University of Texas at Austin
This research was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research award numbers DE-SC0014156 (to TEJ) and DE-SC0017883 (to DBL; USDA-DOE Plant Feedstocks Genomics for Bioenergy). Funding was provided by a National Science Foundation Plant Genome Research Program Awards (IOS-0922457 and IOS-1444533) to TEJ. This research was also based upon work supported in part by the Great Lakes Bioenergy Research Center, U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research under Award 1024 Numbers DE-SC0018409 and DE-FC02-07ER64494. The work conducted by the US Department of Energy Joint Genome Institute, a DOE Office of Science User Facility, is supported by the Office of Science of the US Department of Energy under contract no. DE-AC02-05CH11231.
- Lowry DB et al. QTL x environment interactions underlie adaptive divergence in switchgrass across a large latitudinal gradient. Proc Natl Acad Sci U S A. 2019 June 10. doi:
- GLBRC News Release: “Switchgrass hybrid yields insights into plant evolution”
- JGI Plant Program
- JGI Community Science Program
- CSP 2016 Proposal: Exploring natural genetic diversity in switchgrass (Panicum virgatum) and its microbiome
- Switchgrass genome on JGI Plant Portal Phytozome
by Massie S. Ballon