Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New RNA polymerase discovered in plants

11.02.2005


Plays roles in flowering, methylation



Biologists at Washington University in St. Louis have discovered an entirely new cellular "machine" in plants that plays a significant role in plant flowering and DNA methylation, a key chemical process essential for an organism’s development. A team headed by Craig Pikaard, Ph, D., Washington University professor of biology in Arts & Sciences, has discovered a fourth kind of RNA polymerase found only in plants and speculated to have been a plant feature for more than 200 million years.

RNA polymerase is an enzyme, or protein machine, essential for carrying out functions of cells and for expression of biological traits. It does its job by copying a template of DNA genetic information in order to make RNAs that encode proteins or that function directly in the cell.


Biologists have studied three kinds of RNA polymerase for decades in organisms ranging from brewer’s yeast to humans. In all eukaryotes, the RNA polymerases Pol I, II, and III perform the same distinct , though separate, functions in different species.

But then along came Pol IV. Pikaard first noticed the evidence for a fourth polymerase when analyzing gene sequences after Arabidopsis thaliana , the "laboratory rat" of the plant world, was sequenced in 2001. It originally looked to him like an alternative form of either Polymerase I (Pol I), which makes the largest of the ribosomal RNAs, Pol II which makes RNAs for protein-coding genes, or Pol III, a specialist in making the shortest of the ribosomal RNAs and tRNAs.

The big ’subunit’

He and his colleagues looked specifically at two polypeptides that would be the key subunits if the fourth polymerase were functional, namely the largest and second largest subunits, what Pikaard refers to as the catalytic, or "business end" of any known polymerase.

"So, we took a reverse-genetics approach" said Pikaard. " We thought: ’What happens if we knock these genes out?’ So, we knocked out the genes responsible for these subunits and there were no huge consequences. The plants survived, but there were slight delays in flowering and some strange floral defects. The plants were having trouble with organ identity – stamens tried to turn into petals, for instance. Our first hypothesis was that the fourth polymerase was involved with what are known as micro RNAs, which are known to regulate flower development, but that proved wrong."

In a series of genetic and biochemical tests , Pikaard and his collaborators discovered that Pol IV does not share in the duties of Pol I, II or III. But when the Pol IV subunits are knocked out, the most tightly packed DNA in the nucleus becomes less condensed, small RNAs called siRNAs corresponding to highly repeated 5S rRNA genes and retrotransposons (jumping genes) are completely eliminated and DNA methylation at 5S genes and retrotransposons is lost.

Methylation is a vital process involving a chemical modification in cytosine, one of the four chemical subunits of DNA. Without proper DNA methylation, higher organisms from plants to humans have a host of developmental problems, from dwarfing in plants to tumor development in humans to certain death in mice.

Pikaard thinks that Pol IV helps make siRNAs that then direct DNA methylation to sequences matching the siRNAs.

The results were published in Cell online, Feb. 10, 2005 and will appear in the March, 2005 print version of the journal. "Pol IV is somehow involved in maintaining the integrity of the Arabidopsis genome, principally in keeping the silent DNA silent," Pikaard said. "Plants can get by without Pol IV, whereas they can’t do without the other three. We don’t see anything obviously like Pol IV in any other genome, but it’s possible it might have been overlooked."

While Pikaard and his collaborators have indirect evidence that Pol IV is a distinct RNA polymerase, they still have many aspects of Pol IV to unravel. "We know what happens when its gone, but not how it behaves, at this point," he said. "We don’t know its template, or what kind of RNA – long or short – it makes. Presumably, because it is inherently different from the other RNA polymerases, the rules of activity are different for Pol IV."

Pikaard said the Pol IV has a perfect match in rice, the only other plant genome to be sequenced, despite rice being a monocotyledon and Arabidopsis a dicotyledon. "These two plants diverged 200 million years ago, and there is some speculation that this form of polymerase might extend twice as far back in evolution,’ Pikaard said.

Pikaard said that it is strange that so far this kind of polymerase has been found only in plants. "Why would plants only have these?" he questioned. "It is a bit of a mystery how other organisms that use small RNAs and that also do methylation get by without a Pol IV. It might be possible that they have something equivalent, and maybe we haven’t looked hard enough. "

Tony Fitzpatrick | EurekAlert!
Further information:
http://www.wustl.edu

More articles from Life Sciences:

nachricht Switch-in-a-cell electrifies life
18.12.2018 | Rice University

nachricht Plant biologists identify mechanism behind transition from insect to wind pollination
18.12.2018 | University of Toronto

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Data storage using individual molecules

Researchers from the University of Basel have reported a new method that allows the physical state of just a few atoms or molecules within a network to be controlled. It is based on the spontaneous self-organization of molecules into extensive networks with pores about one nanometer in size. In the journal ‘small’, the physicists reported on their investigations, which could be of particular importance for the development of new storage devices.

Around the world, researchers are attempting to shrink data storage devices to achieve as large a storage capacity in as small a space as possible. In almost...

Im Focus: Data use draining your battery? Tiny device to speed up memory while also saving power

The more objects we make "smart," from watches to entire buildings, the greater the need for these devices to store and retrieve massive amounts of data quickly without consuming too much power.

Millions of new memory cells could be part of a computer chip and provide that speed and energy savings, thanks to the discovery of a previously unobserved...

Im Focus: An energy-efficient way to stay warm: Sew high-tech heating patches to your clothes

Personal patches could reduce energy waste in buildings, Rutgers-led study says

What if, instead of turning up the thermostat, you could warm up with high-tech, flexible patches sewn into your clothes - while significantly reducing your...

Im Focus: Lethal combination: Drug cocktail turns off the juice to cancer cells

A widely used diabetes medication combined with an antihypertensive drug specifically inhibits tumor growth – this was discovered by researchers from the University of Basel’s Biozentrum two years ago. In a follow-up study, recently published in “Cell Reports”, the scientists report that this drug cocktail induces cancer cell death by switching off their energy supply.

The widely used anti-diabetes drug metformin not only reduces blood sugar but also has an anti-cancer effect. However, the metformin dose commonly used in the...

Im Focus: New Foldable Drone Flies through Narrow Holes in Rescue Missions

A research team from the University of Zurich has developed a new drone that can retract its propeller arms in flight and make itself small to fit through narrow gaps and holes. This is particularly useful when searching for victims of natural disasters.

Inspecting a damaged building after an earthquake or during a fire is exactly the kind of job that human rescuers would like drones to do for them. A flying...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

ICTM Conference 2019: Digitization emerges as an engineering trend for turbomachinery construction

12.12.2018 | Event News

New Plastics Economy Investor Forum - Meeting Point for Innovations

10.12.2018 | Event News

EGU 2019 meeting: Media registration now open

06.12.2018 | Event News

 
Latest News

Physicists found a correlation between the structure and magnetic properties of ceramics

18.12.2018 | Physics and Astronomy

Unique insights into an exotic matter state

18.12.2018 | Physics and Astronomy

Physicists studied the influence of magnetic field on thin film structures

18.12.2018 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>