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Subtitree: an award-winning project focused on controlling canker stain of plane trees

The plane trees that border the Canal du Midi are affected by a disease called canker stain. Their removal is the only control method available at present.  The objective of Subtitree, a project led by INRA and the LISBP1 and supported by TWB2  was to design and obtain a living organism capable of controlling this fungus.  The results of this work won a special award at the IGEM3 competition organised by MIT4.

canker plane. © INRA
Updated on 02/25/2016
Published on 03/02/2015

Subtitree: a project focused on a local issue, canker stain of plane trees

This disease is caused by a pathogenic fungus (Ceratocystis platani), which is rife in the Midi-Pyrénées region and notably along the banks of the Canal du Midi, which since 1996 has been qualified as a UNESCO World Heritage Site.  To date, no curative solution has proved its worth, and the only answer has been the prophylactic removal of affected trees and those around them.  At this rate, between now and 15 to 20 years hence, all trees will have been cut down along the banks of the canal.


Synthetic biology comes to the aid of plane trees

In the context of an international competition in the field of synthetic biology, organised annually by MIT, 11 students from two schools in Toulouse (INSA and Université Paul Sabatier) decided to give themselves nine months to design and obtain a biological system endowed with a new and innovative function.  The Bacillus subtilis bacterium, which is naturally present in trees, was modified to meet three scientific imperatives: targeting (chemotactic movement of the bacterium towards the site of infection), binding of the bacterium to the wall of the pathogen, and destruction (production of three antifungal substances by the bacterium).


The concept of a new living organism, tested and validated by INRA in Auzeville

In such a short time, the project has not yet found a response to the problem of dissemination.  However, the students have reflected on this issue and proposed the following improvements: the bacterium must be seasonal and must not sporulate (i.e. must not become dormant in winter), it must be dependent on proline (an amino acid present in tree sap but absent from the soil) and it must not be able to transmit its gene pool to other bacteria (transfer system prevented by the production of a toxin that destroys the recipient bacterium).  In view of the virulence of the canker fungus, the team, supervised by research scientists and teachers, were able to prove the efficacy of this bacterium on pathogenic species genetically similar to Ceratocystis platani.

Subtitree, an award winner at the MIT competition, which still requires precautions for use

Rewarded by IGEM for the quality of the work, its experimental approach and the production of BioBricks (DNA fragments), the project remains nevertheless at a very upstream stage in its development.  Indeed, it is still necessary to ensure the very great specificity of the bacterium in the context of a targeted attack, its non-viability in nature and its death each year.  Supported by numerous public and private partners (and notably by the company ADISSEO) and the TULIP Laboratory of Excellence, this project offers research perspectives in the context of a doctoral thesis.

1 LISBP: INRA-CNRS-INSA Joint Research Unit for the Engineering of Biological  Systems and Processes
2 TWB: Toulouse White Technology
3 IGEM: International Genetically Engineered Machine
4 MIT: Massachusetts Institute of Technology

For further information