How a tomato plant foils a dreaded vampire vine

Forget garlic. In real life, a tomato can defeat a vampire. And researchers have now figured out the first step to vegetable triumph.

The vampires are slim, tangling vines that look like splats of orange or yellow-green spaghetti after a toddler’s dinnertime tantrum. Botanically, the 200 or so Cuscuta species are morning glories gone bad. In the same family as the heavenly blue garden trumpets, the dodders, as they’re sometimes called, lose their roots about a week after sprouting and never grow real leaves. Why bother when you can drain food and water from the neighbors?
A dodder seedling, basically a bare stem, finds that first neighbor by writhing and groping (in slow plant time) toward attractive plant odors. “The Cuscuta can smell its victims,” says Markus Albert of the University of Tübingen in Germany.

Depending on the dodder species, victims include asparagus, melons, sugar beets, petunias, garlic, chrysanthemums and oak trees. Even worse for civilization as we know it, some Cuscuta species vampirize coffee plants and grapevines.
Certain dodders do kill tomato plants. But not the C. reflexa from Asia that Albert studies; instead, it gets its skinny little haustoria whipped. Haustoria are the organs that make plant parasitism possible. When a dodder seedling brushes against tasty prey, a haustorium disk forms and pushes out from the dodder stem with a fast-growing point. “It really looks like a vampire tooth,” Albert says.

If the prey is, say, a soybean plant, it’s doomed. The growing dodder haustorium not only exerts force but also releases enzymes that weaken the bean’s tissue. Haustorium tip cells send out projections that grasp the bean’s inner ducts for water and nutrients, diverting so much that the bean starves.

A tomato plant poked by a haustorium, however, panics. A patch of cells on the stem elongate and burst, forming a scab that stops the intruder. The haustorium stalls and eventually dies.

A gene called CuRe1 lets the tomato recognize the dodder as a dire threat, Albert and colleagues report in the July 29 Science. They transferred the gene to a normally susceptible relative and — Ha! Bite that, vampire! Albert predicts additional biochemistry could be needed to dodder-proof other crops. But for starters, researchers now know the first step in protection: A tomato’s rare power to survive a scary vampire is the ability to get really scared itself.