Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


New RNA polymerase discovered in plants


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:

More articles from Life Sciences:

nachricht The gene of autumn colours
27.10.2016 | Hokkaido University

nachricht Polymer scaffolds build a better pill to swallow
27.10.2016 | The Agency for Science, Technology and Research (A*STAR)

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Etching Microstructures with Lasers

Ultrafast lasers have introduced new possibilities in engraving ultrafine structures, and scientists are now also investigating how to use them to etch microstructures into thin glass. There are possible applications in analytics (lab on a chip) and especially in electronics and the consumer sector, where great interest has been shown.

This new method was born of a surprising phenomenon: irradiating glass in a particular way with an ultrafast laser has the effect of making the glass up to a...

Im Focus: Light-driven atomic rotations excite magnetic waves

Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion

Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...

Im Focus: New 3-D wiring technique brings scalable quantum computers closer to reality

Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...

Im Focus: Scientists develop a semiconductor nanocomposite material that moves in response to light

In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.

A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...

Im Focus: Diamonds aren't forever: Sandia, Harvard team create first quantum computer bridge

By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.

"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...

All Focus news of the innovation-report >>>



Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

Agricultural Trade Developments and Potentials in Central Asia and the South Caucasus

14.10.2016 | Event News

World Health Summit – Day Three: A Call to Action

12.10.2016 | Event News

Latest News

The gene of autumn colours

27.10.2016 | Life Sciences

Polymer scaffolds build a better pill to swallow

27.10.2016 | Life Sciences

Greater Range and Longer Lifetime

26.10.2016 | Power and Electrical Engineering

More VideoLinks >>>