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Cataloguing Natural Pesticides' Modes of Action

By Luis Pons
November 17, 2004

Precisely how genes in fungi and weeds respond to natural pesticides, and cataloguing these responses, is the focus of cutting-edge studies by Agricultural Research Service scientists in Oxford, Miss.

Plant physiologist Stephen O. Duke, molecular biologist Scott Baerson and plant molecular geneticist Zhiqiang Pan at the ARS Natural Products Utilization Research Unit are using gene microarray technology to study how natural fungicides and herbicides affect a genetic process called transcription.

Most genes are expressed as proteins. Transcription is the first of two stages most genes undergo during this process. During transcription, genetic information from DNA is transferred to messenger RNA (mRNA). The second step, in which mRNA data is transferred to the protein, is called translation.

The researchers are currently cataloguing the effects, called "modes of action" or MOAs, of natural fungicides and herbicides on genes. This information will be gathered in a gene transcription library for fungicides. A similar library for herbicides will eventually be assembled, according to Duke.

Over time, plants and fungi have developed resistance to many agricultural pesticides, creating a need for the discovery of biologically based compounds, or biocides, with new modes of action.

Organisms treated with pesticides respond by altering the transcription of their genes, and different pesticides cause different transcription patterns. The results are "transcription fingerprints" that can be documented and catalogued.

According to Duke, libraries of these "fingerprints" will make it possible to screen new biocides whose MOAs are unknown, to see if their fingerprints are similar to those of other known MOAs and thus warrant further testing. Also, the approach can help researchers identify previously unknown targets of novel biocides, based on which genes are affected by the compound.

DNA microarray technology helps to identify MOAs because it simultaneously provides transcription data for every gene in an organism.

Any libraries developed will be publicly available once they are considered reliable. But Duke stressed that much work still needs to be done.

ARS is the U.S. Department of Agriculture's chief scientific research agency.