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 Nanoparticle Exposure Can Awaken Dormant Viruses in the Lungs
16.01.2017 | Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt

nachricht Cholera bacteria infect more effectively with a simple twist of shape
13.01.2017 | Princeton University

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

Im Focus: Bacterial Pac Man molecule snaps at sugar

Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.

The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...

Im Focus: Newly proposed reference datasets improve weather satellite data quality

UMD, NOAA collaboration demonstrates suitability of in-orbit datasets for weather satellite calibration

"Traffic and weather, together on the hour!" blasts your local radio station, while your smartphone knows the weather halfway across the world. A network of...

Im Focus: Repairing defects in fiber-reinforced plastics more efficiently

Fiber-reinforced plastics (FRP) are frequently used in the aeronautic and automobile industry. However, the repair of workpieces made of these composite materials is often less profitable than exchanging the part. In order to increase the lifetime of FRP parts and to make them more eco-efficient, the Laser Zentrum Hannover e.V. (LZH) and the Apodius GmbH want to combine a new measuring device for fiber layer orientation with an innovative laser-based repair process.

Defects in FRP pieces may be production or operation-related. Whether or not repair is cost-effective depends on the geometry of the defective area, the tools...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

Multiregional brain on a chip

16.01.2017 | Power and Electrical Engineering

New technology enables 5-D imaging in live animals, humans

16.01.2017 | Information Technology

Researchers develop environmentally friendly soy air filter

16.01.2017 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>