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Pradeep Kachroo: Helping Plants Defend Themselves

by Jeff Worley
Photo by Alicia P. Gregory

To say that Pradeep Kachroo has had a longtime love affair with plants is an overstatement. But only slightly.

"I like plants. I like to be with plants. They're easy to get along with and although they don't say much," he says with a smile, "they have their subtle ways of indicating displeasure."

Photo of Pradeep KachrooKachroo realized this interest in plants in his mid-teens, and he has followed that interest ever since. A native of India, he came to the United States in 1993 to study at the University of Wisconsin in Madison and earned a doctorate there in microbiology in 1995.

Then, after working at two research institutes in the United States, Kachroo joined the UK faculty in 2002 as an assistant professor in the Department of Plant Pathology. He enjoys working in his second-floor lab in UK's new plant science building, he says, where he and his team of researchers are focusing on plant defense systems and how they function.

"Specifically, what we're trying to do is figure out what makes plants resistant," he says. Kachroo and his crew are trying to determine exactly what happens when a pathogen lands on a plant. And in this confrontation, time really is of the essence. When an invader achieves touchdown, the clock starts running—for both plant and pathogen. "Plants have always had some means to defend themselves. It's just that some don't recognize their microbial attackers in time."

Whether or not a plant marshals its defenses in time to thwart the attack has to do with signaling processes, Kachroo explains. "Signaling processes involve cells talking with each other and the components within cells talking with each other." What these cells "say" to one another is the focus of Kachroo's research, and he admits that finding the answers to plantly communication is far from easy.

"These signaling processes are highly complex, and we have yet to make a dent in understanding them," he says. "How do they work to make the plant immune to a particular pathogen? If we can understand the signaling pathways that make the difference between a resistant and a susceptible plant, we could manipulate these pathways to get resistance. That is our basic aim." In their work, the researchers are using Arabidopsis as a model plant system, since any information they get from this well-studied plant can be applied to other plant systems and crops.

Plants resist pathogen infection by inducing a defense response that manifests itself in localized cell death at the site of pathogen entry, a process that often is able to restrict the spread of pathogen. This phenomenon is known as the hypersensitive response.

Concurrent with hypersensitive response development, Kachroo explains, is a triggering of defense reactions locally and in parts distant from the site of primary infection. This phenomenon, known as systemic acquired resistance, is one of the most studied defense responses and is accompanied by a local and systemic increase in endogenous salicylic acid (SA), which sets off a number of defense genes.

"People aren't the only ones who benefit from salicylic acid, the active ingredient in aspirin," Kachroo says. "Research has shown that spraying this naturally occurring compound onto some plants triggers natural defenses that keep harmful fungi, bacteria, and viruses at bay." He and other plant researchers focus their work on SA, he says, because spraying it on plants snaps them to attention and puts their defenses on high-alert against attacks.

Recently, Kachroo and his team have zeroed in on another signaling system, one that has eluded scientists until now.

"We've found another signaling pathway that may allow plants to respond to a pathogen, and it involves fatty acids," Kachroo says. "So far, we've identified several different aspects of fatty acid signaling in plants, and we're following this line of research. The main thing we've learned is that there is an interconnection between salicylic acid and jasmonic acid, another important cell regulator that mediates defense responses in plants, and that fatty acids are involved in the 'cross talk' between the two."

The more that is known about signaling pathways, the greater possibility for researchers to design an "on/off" switch for specific plants. "If we can do that, we can turn on these pathways," Kachroo. "Then we'd be better able to control the health of the plants."

When pressed to say what excites him most about working with plants, Kachroo pauses, then says, "For me it's the fact that you can discover and understand so much of the invisible world. Each experiment we do is exciting because we learn something at every step—many things we didn't expect to discover. It keeps us fresh."