Nature is not just out to kill us, it is out to kill itself, in the interest of surviving over the long term. That is why even the most wholesome backyard organic garden is a hotbed of combat between plants and unseen microorganisms in the soil fighting for space to grow.

To defeat a plant, a microbe might produce and use toxic chemicals - but then the microbe also needs immunity from its own poisons. The genes that create protective shield in microorganisms could become a new, highly effective weed killer and the first new class of commercial herbicides in more than 30 years.

It's needed. Pests of all kinds have always struggled to keep up with science, so even the best product will lead to resistance. Products like copper sulfate are barely useful now, organic gardeners have to use a lot of it with environmental consequences, whereas more useful products like glyphosate are often mixed to avoid creating resistance. A natural weed killer satisfies the organic camp and the science one.

The new herbicide was discovered using resistance gene-directed genome mining - searching the genes of thousands of fungi for one that might provide immunity against fungal poisons. 

Herbicide molecule (top), which inhibits an enzyme (bottom) that plants need. Credit: Tang Research Group / UCLA Samueli

"Microorganisms are very smart at protecting themselves from the potent molecules they make to kill their enemies," said UCLA Proessor Yi Tang,  co-principal investigator, in a statement. "The presence of these resistance genes provides a window into the functions of the molecules, and can allow us to discover these molecules and apply them to diverse applications in human health and agriculture."

if a resistance gene that protects a microorganism from an anti-bacterial product is found, there's a possibility that the microorganism also has genes to produce that same anti-bacterial compound. That discovery could potentially lead to new antibacterial medicines.

The new herbicide acts by inhibiting the function of an enzyme that is necessary for plants' survival. The enzyme is a key catalyst in an important metabolic pathway that makes essential amino acids. When this pathway is disrupted, the plants die.

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This pathway is not present in mammals, including humans, which is why it has been a common target in herbicide research and development. The new herbicide works on a different part of the pathway than current herbicides. Because they discovered the new herbicide and its exact target in the plant, it opens the possibility of modifying crops to be resistant to a commercial product based on this herbicide.

To confirm the efficacy of the new herbicide, the team tested the fungus-produced product on a common plant used in lab studies called Arabidopsis. In experiments, the product killed the plants after they were sprayed with it. The researchers also implanted the resistance gene from the fungus into Arabidopsis genomes. The plants that had the resistance gene implanted in them were immune to the herbicide.