Nav: Home

Counting chromosomes: Plant scientists solve a century-old mystery about reproduction

January 18, 2018

Cold Spring Harbor, NY - Counting is vital in nature. Counting chromosomes is something that most animals, plants and even single-celled organisms need to know how to do to assure viability and to reproduce. Today, a team of geneticists reveals a remarkable mechanism that enables plants to count their chromosomes, solving a century-old mystery.

Being able to count the amount of genetic material in a given cell or organism is a prime factor in ensuring that each cell receives the same complement of genes after each cell division. In plants, the mechanism that prevents individuals with imbalances in chromosome number from reproducing is something scientists call "the triploid block."

The mechanism behind this classical problem now has been solved by Professor Rob Martienssen of Cold Spring Harbor Laboratory (CSHL) and the Howard Hughes Medical Institute, and a team led by Filipe Borges, a postdoctoral researcher in his lab, with Dr. Claudia Köhler and colleagues at the University of Uppsala in Sweden.

Their research stems from the knowledge that chromosomes are covered with transposable elements (TEs), commonly called jumping genes. This raised the question, says Martienssen, "of whether a cell might be able to detect and count transposons as a proxy for chromosomes."

One way of doing so, he reasoned, might have to do with small RNA molecules, which are generated by cells to keep potentially mutagenic transposons from becoming active.

Martienssen and Borges discovered a special kind of small RNA molecule found only in the pollen of flowering plants, called microRNA 845 (miR845). In a series of experiments reported in Nature Genetics the team now shows that miR845 seeks out and targets most transposons in plants genomes, triggering synthesis of secondary small RNAs called easiRNAs (epigenetically activated small interfering RNAs).

The more chromosomes a pollen grain has, the more transposons, and therefore the more easiRNAs it accumulates in its sperm. When the sperm unites with the female gametes (eggs) in a developing seed, a kind of counting ensues. If the "dosage" of chromosomes and easiRNAs is far out of balance, it triggers the triploid block and the seed collapses.

The team proposes a mechanism behind this block, as easiRNAs are able to silence key genes called imprinted genes on both the maternal and paternal sides. Such silencing results in the sterilization of the emerging seed. The discovery adds to basic biological understanding of chromosome regulation. It could also be a boon to plant breeders, who, explains Martienssen, would like to figure out ways to get around the triploid block, to cross otherwise reproductively incompatible plants.
-end-
Funding: National Institutes of Health; National Science Foundation Plant Genome Research Program; Howard Hughes Medical Institute and Gordon and Betty Moore Foundation; CSHL Cancer Center Support Grant; European Research Council Starting Independent Researcher grant; Swedish Science Foundation; Knut and Alice Wallenberg Foundation; Marie Curie IOF Postdoctoral Fellowship.

Citation: Borges, F et al, "Transposon-derived small RNAs triggered by miR845 mediate genome dosage response in Arabidopsis" appeared online in Nature Genetics January 15, 2018.

About Cold Spring Harbor Laboratory


Founded in 1890, Cold Spring Harbor Laboratory has shaped contemporary biomedical research and education with programs in cancer, neuroscience, plant biology and quantitative biology. Home to eight Nobel Prize winners, the private, not-for-profit Laboratory employs 1,100 people including 600 scientists, students and technicians. The Meetings & Courses Program annually hosts more than 12,000 scientists. The Laboratory's education arm also includes an academic publishing house, a graduate school and the DNA Learning Center with programs for middle and high school students and teachers. For more information, visit http://www.cshl.edu

Cold Spring Harbor Laboratory

Related Chromosomes Articles:

X marks the spot: recombination in structurally distinct chromosomes
A recent study from the laboratory of Stowers Investigator Scott Hawley, PhD, has revealed more details about how the synaptonemal complex performs its job, including some surprising subtleties in function.
How chromosomes change their shape during cell differentiation
Scientists from the RIKEN Center for Biosystems Dynamics Research have provided an explanation of how chromosomes undergo structural changes during cell differentiation.
Key similarities discovered between human and archaea chromosomes
A study led by Indiana University is the first to reveal key similarities between chromosomes in humans and archaea.
Science snapshots: Chromosomes, crystals, and drones
From Berkeley Lab: exploring human origins in the uncharted territory of our chromosomes; scientists grow spiraling new material; drones will fly for days with this new technology
Human artificial chromosomes bypass centromere roadblocks
Human artificial chromosomes (HACs) could be useful tools for both understanding how mammalian chromosomes function and creating synthetic biological systems, but for the last 20 years, they have been limited by an inefficient artificial centromere.
Does rearranging chromosomes affect their function?
Molecular biologists long thought that domains in the genome's 3D organization control how genes are expressed.
Super-resolution microscopy illuminates associations between chromosomes
Thanks to super-resolution microscopy, scientists have now been able to unambiguously identify physical associations between human chromosomes.
B chromosome first -- mechanisms behind the drive of B chromosomes uncovered
B chromosomes are supernumerary chromosomes, which often are preferentially inherited and showcase an increased transmission rate.
Dark centers of chromosomes reveal ancient DNA
Geneticists exploring the dark heart of the human genome have discovered big chunks of Neanderthal and other ancient DNA.
Reading the dark heart of chromosomes
A new study publishing May 14, 2019 in the open-access journal PLOS Biology by the Mellone lab at the University of Connecticut and the Larracuente lab at the University of Rochester combine cutting-edge sequencing technology with molecular and high-resolution microscopy methods to discover the sequences of all centromeres in the fruit fly Drosophila melanogaster, a powerful model organism widely used in biomedical research.
More Chromosomes News and Chromosomes Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

Risk
Why do we revere risk-takers, even when their actions terrify us? Why are some better at taking risks than others? This hour, TED speakers explore the alluring, dangerous, and calculated sides of risk. Guests include professional rock climber Alex Honnold, economist Mariana Mazzucato, psychology researcher Kashfia Rahman, structural engineer and bridge designer Ian Firth, and risk intelligence expert Dylan Evans.
Now Playing: Science for the People

#541 Wayfinding
These days when we want to know where we are or how to get where we want to go, most of us will pull out a smart phone with a built-in GPS and map app. Some of us old timers might still use an old school paper map from time to time. But we didn't always used to lean so heavily on maps and technology, and in some remote places of the world some people still navigate and wayfind their way without the aid of these tools... and in some cases do better without them. This week, host Rachelle Saunders...
Now Playing: Radiolab

Dolly Parton's America: Neon Moss
Today on Radiolab, we're bringing you the fourth episode of Jad's special series, Dolly Parton's America. In this episode, Jad goes back up the mountain to visit Dolly's actual Tennessee mountain home, where she tells stories about her first trips out of the holler. Back on the mountaintop, standing under the rain by the Little Pigeon River, the trip triggers memories of Jad's first visit to his father's childhood home, and opens the gateway to dizzying stories of music and migration. Support Radiolab today at Radiolab.org/donate.