Potential new herbicide

The contentious matter of plant GM (genetic manipulation – which always sounds more menacing and mankind-meddling-with-nature than GE, genetic engineering, or the other GM – genetic modification…) has been put in the spotlight recently with Gilles-Eric Séralini et al.’s paper. Entitled ‘Long term toxicity of a Roundup herbicide and a Roundup-tolerant genetically modified maize’, it ascribes health and ‘longevity-shortening’ (i.e. earlier deaths…) effects in rats not only to the endocrine-disrupting effects of Roundup (commercial name for glyphosate, a herbicide), but also the over-expression of the transgene for glyphosate tolerance in GM maize and its metabolic consequences. Strong stuff indeed, and which has caused not a little concern and understandable ‘interest’ amongst the media (e.g. prompting a press release by the European Food Safety Authority and an article from the Agricultural and Rural Convention).

Leaving aside considerations about what this episode might tell us about the process of peer-review of scientific research, given the long-standing and enduring interest/concerns about Roundup and GM crops, suggestion of an alternative to glyphosate will probably be welcomed. Encouraging news then that Sarah Barry et al. have elucidated a key step in production of thaxtomin. Thaxtomin, which exhibits herbicidal activity by inhibiting cellulose biosynthesis and thus interfering with formation of plant cell walls, is made naturally by Streptomyces species, actinomycetous bacteria that cause the disease known as potato scab. Although thaxtomin’s herbicidal nature has been known for some time, its commercialisation was not realistically possible without fuller understanding of its biosynthetic pathway. With Berry et al.‘s identification of the particular P450 cytochrome enzyme – TxtE – that catalyses an important step in thaxtomin synthesis, it is expected that the phytocide might now be made in amounts that could be commercially exploited. And, as a ‘natural product’, it is apparently able to be used in agricultural systems that have the cachet (to say nothing of any ‘sales-price-premium’) accorded by their ‘organic’ status/certification. (But probably best not to dwell on the fact that commercial amounts of this natural, organic herbicide may need to be produced by GM’d bacteria.)