DURHAM, N.C. Timing is everything in the long-standing arms race between the flowering plant Arabidopsis and Hyaloperonospora, a downy mildew pathogen.
Duke University researchers have found that the little mustard plant cranks up its immune system in the morning to prepare for the greatest onslaught of infectious spores released by the mildew.
It isn't news that plants know what time of day it is and change their activities accordingly, but this is the first time that a plant's defensive systems have been shown to cycle on a daily basis even when pathogens aren't present. Their work appears in the Feb. 3 edition of Nature.
The powerful chemical compounds Arabidopsis uses to fight mildew infection are expensive to make and also potentially harmful to the plant itself over the long-term, so a daily, or circadian, cycle of production is safer and more efficient than simply having the chemicals on hand all the time, said Duke biology professor Xinnian Dong.
Morning, just as the dew dries, is the right time to have defenses at the ready.
When the mildew has been able to successfully set up housekeeping within Arabidopsis, it produces a flowering body that grows upward from the leaf surface. Bearing its spores for the next generation, it looks very much like a tree covered with apples. As the morning dew dries from the leaf, the mildew's flowering body twists violently, flinging the tiny spores in all directions to be carried on air currents until they settle on a potential new host.
Other researchers who have collected the spores had noted that the morning was the most productive time to catch them, but Arabidopsis apparently already knew that.
Dong and her graduate students Wei Wang and Jinyoung Barnaby discovered this surprising circadian clock connection during a more general search of Arabidopsis immune system genes. They found 22 candidate genes th
|Contact: Karl Leif Bates|