It’s simple to overlook what takes place underground in a cornfield, but corn root architecture can have a significant impact on water and nutrient uptake, impacting drought resistance, water use effectiveness, and sustainability. If corn roots grew down at a steeper angle, they might be able to reach valuable resources that are deeper in the soil.
Learning the genes responsible for gravitropism, or root growth in response to gravity, is a first step toward achieving that goal. Researchers from the University of Wisconsin and the University of Illinois identified four such genes in the model plant Arabidopsis and corn in a recent study that was published in the Proceedings of the National Academy of Sciences.
Some roots of a germination seed turn abruptly and steeply in the direction of gravity, while others turn slightly more slowly. The researchers combined the data with genetic information for each seedling after using machine vision techniques to detect minute variations in root gravitropism in thousands of seedlings. The outcome depicted the genome’s most likely locations for gravitropism genes.
The map led the scientists to the appropriate regions of the genome, each containing a few hundred genes, but they were still a long way from pinpointing the precise genes responsible for gravitropism. Fortunately, they had a resource at their disposal.
“We matched genes within the relevant regions of the genome in both species because we had previously carried out the same experiment with the distantly related Arabidopsis plant. Four genes that alter root gravitropism have had their identities confirmed by subsequent tests. The new data might clarify how gravity affects roots system architecture, “Edgar Spalding, a professor in the University of Wisconsin’s Department of Botany and the study’s lead author, says.”
Professor Matt Hudson, co-author of the study and chair of the Department of Crop Sciences at the University of Illinois, continues, “We examined a trait of maize that has received little attention but is crucial for many reasons, particularly in light of climate change. And we accomplished this by taking advantage of the ways that plants evolve differently from one another.
In terms of evolutionary history, corn and Arabidopsis, a tiny mustard relative that plant biologists have thoroughly described, diverged about 150 million years ago. Despite the fact that both species share fundamental plant functions, according to Hudson, the genes in charge of those functions have probably been mixed up within the genome over time. That actually works well for limiting the number of common genes.
Genes typically line up in the genome in roughly the same order in closely related species (e.g., ABCDEF). The genes in the region where the trait maps may be the same in distantly related species, but they are not in the same order (e.g., UGRBZ). The otherwise mismatched gene sequences made the common genes (in this case, B) stand out once the researchers knew where to look in each genome.
By comparing genomic intervals in different plant species, we were able to identify genes that we otherwise would not have discovered, says Hudson. “We were fairly certain of their identity when they immediately emerged from this analysis, but Spalding’s team had to spend another seven or eight years gathering reliable biological evidence to show that they do, in fact, contribute to gravitropism. After completing that, I believe we have validated the entire methodology, allowing you to use it in the future for a wide range of phenotypes. ”
According to Spalding, the technique was probably particularly effective because exact measurements were taken in a typical setting.
He explains that while Arabidopsis researchers typically raise their plants in growth chambers, maize researchers frequently measure their traits of interest in a field. “We conducted a stringently controlled measurement of the root gravitropism phenotype. In contrast to traits you might measure in the real world that are subject to a wide range of variability, these seeds were grown on a petri plate, and the assay only lasted a few hours. ”
Not all traits are good candidates for this method, even when they can be measured in a common setting. So that the same ancient genes exist in species that are not related to each other, the researchers stress that the traits in question should be essential to how plants work.
According to Spalding, gravity may be especially amenable to research using this method because it was crucial to the early specialization of shoots and roots following successful land colonization.
According to Hudson, gravitropism will be essential for colonizing a new environment.
NASA is interested in cultivating plants on other planets or in space, and they want to know what to breed for. Without gravity, plants are rather disorganized.
