Today it's hard to tell that the two plants were ever close kin: Corn plants stand tall, on a single sturdy stalk, and produce a handful of large, kernel-filled ears. By contrast, teosinte is branchy and bushy, with scores of thumb-sized "ears," each containing only a dozen or so hard-shelled kernels.
In seeking to better understand how teosinte gave rise to corn, a scientific team has pinpointed one of the key genetic changes that paved the way for corn's domestication. As reported today (Sept. 25) on the Nature Genetics website, a major change occurred about 23,000 years ago, when a small piece of DNA — a jumping gene known as Hopscotch — inserted itself into the control region of a teosinte gene that affects plant architecture. This case is among the first to show that a jumping gene can cause alterations in gene expression that impact evolution.
"Hopscotch cranked up the gene's expression, which helped the plant produce larger ears with more kernels, plus become less branchy, and so those early farmers picked plants with the Hopscotch to breed," says University of Wisconsin-Madison plant geneticist John Doebley, a corn evolution expert who led the team.
Jumping genes are strange genetic entities. Found in all sorts of organisms, these pieces of DNA, which carry just a few genes, have the ability to splice themselves out of their current position in the genome and "jump" to other spots. As they mix and mingle with the genome, jumping genes, which are also known as transposable elements, create genetic variation that evolution can act upon. Typically, jumping genes' effects are neutral or bad, as when they land in a stretch of junk DNA or disrupt a critical gene.
"But occasionally, they do something good," says Doebley. "So we found a case where the mutation caused by a transposable element has done something good."
In corn, Hopscotch dials up expression of the teosinte branched 1 (tb1) gene, which produces a transcriptional regulator protein that represses branching, encouraging the plant to grow a single stalk and produce larger ears with more kernels. When early Mexican farmers first encountered teosinte with this Hopscotch insertion, the rare plants must have been prized breeding stock: Today 95 percent of modern corn has this particular genetic alteration.
In recent years, researchers have begun finding more and more cases where transposable elements are associated with altered gene expression, but the links are often only correlative. For this project, however, the paper's first author, Anthony Studer, Doebley's former graduate student who now works as a postdoctoral researcher at Cornell, took the time to show that Hopscotch does in fact cause elevated gene expression. In doing so, this study is among the first to prove that jumping genes can impact gene expression, and, in turn, evolution.
"It's rare that geneticists can explain the genetic changes involved in domestication at this level of detail," notes Doebley, who has made a number of impressive contributions to the corn evolution field over the years.
Early in his career, Doebley helped identify teosinte as corn's closest relative, and in 2005, his team showed that a single genetic mutation was responsible for removing the hard casing around teosinte's kernels, exposing soft grain, another critical step in corn's domestication.
While Doebley's motivation comes from the desire to understand basic evolutionary processes, his work, he notes, could also have real-world applications. "People in plant breeding and plant biotechnology take some interest in this work because they are basically trying to continue the domestication process," he explains. "So understanding what's worked in the past could influence what they do in the present to improve corn."
In addition to Doebley and Studer, the Nature Genetics paper's authors include Qiong Zhao, a graduate student in Doebley's lab, and Jeffrey Ross-Ibarra, an assistant professor of plant sciences at the University of California, Davis.
The work was funded through a U.S. Department of Agriculture Hatch grant and by the National Science Foundation.
— Nicole Miller, email@example.com, 608-262-3636
John Doebley | EurekAlert!
Rainbow colors reveal cell history: Uncovering β-cell heterogeneity
22.09.2017 | DFG-Forschungszentrum für Regenerative Therapien TU Dresden
The pyrenoid is a carbon-fixing liquid droplet
22.09.2017 | Max-Planck-Institut für Biochemie
Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.
A warming planet
Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...
Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...
Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!
When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...
For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.
Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...
19.09.2017 | Event News
12.09.2017 | Event News
06.09.2017 | Event News
22.09.2017 | Life Sciences
22.09.2017 | Medical Engineering
22.09.2017 | Physics and Astronomy