Arabidopsis Anticipates Mildew Attack in the Morning

Wei Wang of Duke University and colleagues discovered that Arabidopsis cranks up its immune system in the morning in preparation for the greatest infestation of spores from Hyaloperonospora, a downy mildew. This is the first finding about the plant's defense system cycling on a daily basis even in the absence of pathogens. Since it is expensive to produce chemical compounds that protects Arabidopsis from downy mildew, thus a circadian cycle of production is safer and more efficient.

Wang discovered this connection between the circadian clock and plant immunity during their general search for genes linked to the immune system of Arabidopsis. They found 22 genes related to immune response to downy mildew and a number of those genes exhibited rhythmic expression patterns. The expression patterns were monitored and they observed that the defense genes are expressed by schedule even in the absence of pathogens. To test this hypothesis, they exposed the plants to mildew spores at dawn and at dusk and infection rates were found to be higher during dusk.

They used "clock mutants" that lack the circadian clock regulator (CCA1) and results show that these mutants had higher infection rates than normal plants.

Read more details at http://www.nature.com/nature/journal/v470/n7332/full/nature09766.html.