The evolution of an invasive plant, Sorghum halepense L. ('Johnsongrass')

Summary

Draft sequencing of a S. halepense genome, together with molecular analysis of 599 Johnsongrass samples sampling most of its continental United States range, are shedding new light on the evolution and biology of this species, toward its control. Surprisingly, several potential benefits of S. halepense for sorghum improvement have also been identified.

Situation

With at least 24 herbicide-resistant biotypes 8, 'Johnsongrass' (Sorghum halepense L. Pers.), is a noxious weed in 20 U.S. states and an invasive species in 16 9, with climate change favoring further spread Its ability to cross with sorghum despite a ploidy barrier 10,11 makes Sh a paradigm for the dangers of crop 'gene escape'. Johnsongrass has a very large climate niche, with favorable growing conditions occurring across all non-Antarctic continents. Due to the high threats it poses to biodiversity, agricultural production, and food security, Johnsongrass is the focus of intense scientific inquiry.

Response

Draft sequencing of a S. halepense genome, together with molecular analysis of 599 Johnsongrass samples sampling most of its continental United States range, are shedding new light on the evolution and biology of this species, toward its control. Surprisingly, several potential benefits of S. halepense for sorghum improvement have also been identified.

Impact

From noble beginnings as a prospective forage, Sorghum halepense (Sh) has the rare distinction of being both an invasive species and one of the world's worst agricultural weeds. A polyploid formed by S. bicolor (Sb) x S. propinquum (Sp) hybridization, by draft sequencing we show Sh to have Sb-enriched genome composition and striking new mutations in 5,957 genes. The spread of Sh may have been facilitated by recent introgression from sorghum, shown to be enriched near quantitative trait loci affecting rhizome development, seed size, and levels of lutein, a protectant from photochemical damage and abscisic acid precursor. Rhizomes, subterranean stems that store carbohydrates and spawn clonal propagules, have growth correlated with reproductive rather than other vegetative tissues, and increase survival of both temperate cold seasons and tropical dry seasons. Rhizomes in Sh are more extensive than those of its rhizomatous progenitor Sp, and have mosaic gene expression including many alleles derived from its non-rhizomatous Sb progenitor. As the first surviving polyploid in its lineage in ~96 million years, synergy between duplicated genes and interspecific hybridity has nurtured genetic diversity that may have facilitated transition by Sh from agricultural to non-agricultural niches, supports its ongoing spread, and opens new doors to sorghum improvement.

State Issue

Sustainability, Conservation, & the Environment

Details

• Year: 2017
• Geographic Scope: National
• County: Clarke
• Program Areas:
  • Agriculture & Natural Resources