Using “physionomics and metabolomics” approaches to discovery of new modes of action. Klaus Grossmann*, Johannes Hutzler, Stefan Tresch BASF SE, Limburgerhof, Germany; and Nicole Christiansen, Ralf Looser, Thomas Ehrhardt metanomics, Berlin, Germany. E-mail: Klaus.grossmann@basf.com

 

Keyword: Herbicide mode of action, metabolic profiling, physiological profiling

 

The search for novel herbicides with new sites or modes of action is an important assignment in crop protection research. However, for active compounds identified in greenhouse screens, the crucial point is to take the most efficient path to determine their target sites. In the literature today, molecular (functional genomics, transcriptomics), biochemical (proteomics), analytical (metabolomics) and physiological (physionomics) approaches are discussed. In particular, the metabolic and physiological response pattern to a herbicide can be viewed as the end result of changes elicited in the molecular and biochemical process chain. These response patterns are highly diagnostic of a herbicide´s mode of action and are therefore in the focus of this talk. At the starting point of mode of action characterization, we use an array of “functional” biotests for comprehensive physiological profiling of herbicidal effects. Together with a set of assays of known target enzymes, this physionomics procedure enables to discriminate known, novel or multiple modes of action of a compound. Moreover, a first clue to a new mode of action is provided with respect to which structural cell component or metabolic pathway a compound is affecting. In the latter case, metabolic profiling (metabolomics) is performed with the use of treated duckweed (Lemna paucicostata) plants. After plant extraction and subsequent GC-MS and LC-MS/MS analyses, changes in tissue levels of ca. 200 identified and 300 unknown analytes are quantified, relative to control. Check for assignment of metabolite changes to profiles of about 150 herbicides from 60 known modes of action is performed with the use of multivariate statistical data analyses. Effects on plant metabolism are visualized in detail in a biochemical pathway view. Distinct metabolite changes in a pathway (“metabolite hot spots”) can direct to the affected enzymatic step and trigger subsequent studies for target identification. Here, metabolite feeding in Lemna and molecular (e.g. mutant resistance screening) and biochemical (e.g. enzyme activity testing) methods are used. The value of this cascade strategy in mode of action identification is exemplified by recent studies on cinmethylin and isoxazoline derivatives including methiozolin, inhibitors of tyrosine aminotransferase as a new herbicide target.