Thaxtomin A: a promising alternative to synthetic herbicides

In times of trouble for the world’s most popular herbicide – namely Bayer / Monsanto’s Roundup – finding alternatives to glyphosate has become a priority for some companies willing to capture this highly valuable market. Besides synthetic herbicides and their derivatives that are being developed in the industry, interest is growing for natural and ‘green’ active molecules. The plant pathogen Streptomyces scabies provides an interesting clue, as its main virulence factor is a phytotoxin called thaxtomin A. This filamentous Gram + bacteria is known as the causing agent of the common scab disease affecting tuber crops. While it was discovered in 1989, thaxtomin’s action mechanisms are still partly unknown. It appears that it targets the plant cell wall, with reports highlighting similarities to the herbicide isoxaben. Despite being highly active in herbicide assays, the phytotoxin is not being used on a large scale for a simple reason: its cost. The low levels of production and high price of culture media components make it too expensive to be commercialized. Studying and engineering genetic regulation networks controlling thaxtomin A production in S. scabies helped us improving production yields while reducing costs. With improvements still to come, thaxtomin A could become economically-viable and thus be a sustainable alternative herbicide.