Plants prepare for spore attack at dawn

Guided by its biological clock, a small plant arms itself against infection during riskiest times. Perhaps our immune responses are also synced with an internal timekeeper.
Written by Janet Fang, Contributor

Plants can anticipate infection and time their immune attack accordingly, new research shows. Understanding that mechanism could help doctors time our own defenses better.

A fungus-like pathogen (Hyaloperonospora arabidopsidis) causes downy mildew disease in the flowering plant Arabidopsis. Studying the plant’s immune system, researchers found a set of defense genes influenced by the plant's biological clock – the 24-hour circadian cycle, just like ours.

In plants, this daily timekeeper regulates photosynthesis, fragrance release, and when to bloom. Their circadian regulator – called circadian clock-associated 1 (CCA1) – also helps plants prepare the timing of their immune response.

In Arabidopsis, the 22 genes connected to infection-resistance were only expressed after evening time, peaking at dawn – when the fungal pathogen normally disperses its spores (pictured).

“From what we know, the pathogen forms spores at night and disseminates them at dawn, so that’s when the infection threat is highest,” says principal investigator Xinnian Dong of Duke University.

The genes were not expressed during the day when the pathogen is unlikely to attack. And when the team released spores at dusk, infection rates were much higher for the unprepared plants.

Arabidopsis plants that don’t have CCA1 also suffered higher infection rates.

The plant chemicals used to fight mildew infection are expensive to make and potentially harmful to the plant itself over the long-term, Dong says, so a daily cycle of production is safer and more efficient than simply having the chemicals on hand all the time.

This is the first time researchers have been able to make a functional connection between the circadian clock and pathogen resistance, Dong says.

And if researchers can sort out the intricacies of the relationship between pathogens and hosts, and their circadian rhythms, practical lessons could be gleaned. For example, pesticide treatments could be timed to have maximum impact.

Or, Dong adds, it may even be possible to determine ideal times for administering medications in humans.

The research was published in Nature yesterday.

Image: Wei Wang, Xinnian Dong lab

This post was originally published on Smartplanet.com

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