Fungal Warfare

WHEN PLANTS are being attacked by fungal pathogens, their only retaliation is an innate immune response that researchers are only beginning to pick apart. Now, teams in Germany and the U.S. are reporting a new molecule involved in this defense, which could inspire the development of new antifungals for the agricultural industry.

Working independently, both groups report that the new protagonist in the fight against fungi is 4-methoxyindol-3-ylmethylglucosinolate (4M-I3G), yet "we have different takes on how the molecule acts in the plant," Frederick M. Ausubel, a plant scientist at Harvard University, says.

Ausubel and his colleagues find that metabolites of 4M-I3G act as a signal in plants to activate the deposition of callose near sites of fungal intrusion (Science, DOI: 10.1126/science.1164627). Callose is a glucan polymer that acts as a physical barrier against pathogens.

At the same time, a team led by Paul Schulze-Lefert of the Max Planck Institute for Plant Breeding Research, in Cologne, Germany, and colleagues report that 4M-I3G metabolites have "direct antimicrobial activity" against fungi, similar to the antimicrobial peptides in mammalian innate immunity, Schulze-Lefert says (Science, DOI: 10.1126/science.1163732).

The two different roles reported for 4M-I3G are not necessarily at odds, since "multifunctionality of small molecules [in plants] is the norm rather than an exception," Schulze-Lefert explains.

The combined work is "a big step forward for understanding what is stopping the plant pathogens," says Jonathan Jones, a senior scientist at the Sainsbury Laboratory, in the U.K., who studies plant immunity. "We now have an additional component in fungal resistance that we did not know about before."

Both groups worked with the model plant Arabidopsis, and both believe that other plants in the same brassinoid family, like rapeseed and cabbage, may also employ 4M-I3G. "The discoveries may open the field to the design of new fungicides," Ausubel notes.

Daniel J. Kliebenstein, a plant biologist at the University of California, Davis, says the work "shows great potential," but he would like to see more proof that the results can be broadly applied to other plant families.