Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Secrets of a rice-killing fungal toxin

27.10.2015

Researchers at the RIKEN Center for Sustainable Resource Sciences (CSRS) have discovered the enzyme needed for synthesis of tenuazonic acid (TeA), a well-known toxin that is produced by multiple types of fungus and affects fruits, vegetables, rice, and other crops. In their study published in Nature Communications, the authors describe how they found the gene for this enzyme, and reveal that its structure is unique among known enzymes.

Mycotoxins are toxic compounds produced by fungi that are not directly involved in growth, development, or reproduction. These secondary metabolites typically colonize crops and are a real economic burden for farmers. TeA is known to be produced by at least three different plant pathogenic fungi, and is associated with spoiling of fruits, vegetables, and food-crops, as well as post-harvest decay.


Rice blast disease resulting from the mycotoxin tenuazonic acid (produced by the fungus Magnaporthe oryzae).

Credit: RIKEN

"Now that we know the gene responsible for biosynthesis of this harmful toxin," notes co-lead author Takayuki Motoyama, "after further testing we might be able to devise a way to regulate its expression and prevent destruction of important crops."

When studying microorganisms like fungus, researchers have found that genes for many secondary metabolites are silent under laboratory conditions, which has made finding them especially difficult. The CSRS group led by Hiroyuki Osada has extensive experience studying secondary metabolites, and the team reasoned that OSM1--a gene associated with responses to environmental stress--might also be related to TeA production in Magnaporthe oryzae, a pathogenic rice fungus.

While wild-type M. oryzae did not yield any TeA, researchers were able to produce it from OSM1 knockout strains. They were also able to produce TeA by culturing wild-type M. oryzae with 1% dimethylsulphoxide, perhaps as a response to the unfavorable environment.

Having two methods to produce TeA in the lab proved invaluable for identifying the gene responsible for its biosynthesis. To do so, the team performed a DNA microarray analysis using the total RNA extracted under the two conditions that yielded TeA. Only one gene was found to be expressed significantly more in these conditions than when no toxin was produced.

Further tests were run to determine whether this gene really is responsible for TeA biosynthesis. First, knocking out this gene yielded a strain that could not produce the toxin, and researchers tentatively renamed the gene TeA synthetase 1--or TAS1. Then, the team created an M. oryzae strain that overexpressed TAS1, and as expected, this strain produced the toxin under normal conditions.

Next, researchers examined the structure of TAS1 and found that it is a hybrid enzyme containing an NRPS region followed by a PKS region. "This was very surprising", explains Motoyama. "It was assumed because of TeA's structure that it would be synthesized by a PKS-NRPS hybrid enzyme. In fact, the order of these regions was totally reversed!" While NRPS-PKS hybrid enzymes have been found in bacteria, TAS1 is the first fungal enzyme for a secondary metabolite to be discovered with an NRPS-PKS structure.

After analyzing how TeA is generated and determining that TAS1 synthesizes it from isoleucine and acetoacetyl-coenzyme A, the researchers searched for homologues in other organisms. While they found several other species of fungi that have genes for homologues sharing the same domain structure, bacterial sources with similar amino acid sequences did not share the same characteristic domain structure. Further research will be needed to find out if this novel enzyme has homologues that biosynthesize other compounds with useful biological functions.

While preventing TeA synthesis might me a goal for crop preservation, TeA also has antitumor, antibacterial, and antiviral properties that could prove beneficial in many situations. Understanding exactly how it is synthesized by TAS1 is therefore an important next step. "Now that we know that the KS domain of TAS1 is unique," notes co-lead author Choong-Soo Yun, "X-ray crystallographic analysis of this domain will be important for uncovering the reaction mechanism."

###

This study was supported in part by the Japanese Science and Technology Research Promotion Program for Agriculture, Forestry, Fisheries, and Food Industry.

reference: Yun CS, Motoyama T, Osada H. Biosynthesis of the mycotoxin tenuazonic acid by fungal NPRS-PKS hybrid enzyme. Nature Communications. doi: 10.1038/ncomms9758

Adam Phillips | EurekAlert!

Further reports about: RIKEN biosynthesis enzyme fungal fungus genes metabolites pathogenic strain structure synthesized wild-type

More articles from Life Sciences:

nachricht Multi-institutional collaboration uncovers how molecular machines assemble
02.12.2016 | Salk Institute

nachricht Fertilized egg cells trigger and monitor loss of sperm’s epigenetic memory
02.12.2016 | IMBA - Institut für Molekulare Biotechnologie der Österreichischen Akademie der Wissenschaften GmbH

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

Im Focus: Fraunhofer ISE Develops Highly Compact, High Frequency DC/DC Converter for Aviation

The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

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

14.10.2016 | Event News

 
Latest News

UTSA study describes new minimally invasive device to treat cancer and other illnesses

02.12.2016 | Medical Engineering

Plasma-zapping process could yield trans fat-free soybean oil product

02.12.2016 | Agricultural and Forestry Science

What do Netflix, Google and planetary systems have in common?

02.12.2016 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>