Dual Internal Clocks Keep Plant Defenses on Schedule

A new study from Duke University shows that time management is not for busy people only -- it's for plants, too. The study shows how two biological clocks work together to help plants deal with intermittent demands such as infections, while maintaining an already-packed daily schedule of activities like growth.

Plant defense and other daily rhythms are thought to be driven by "morning genes" and "evening genes." Proteins made by the morning genes suppress the evening genes at the beginning of the day, but as the proteins start to build up within the cell they eventually turn themselves off. The subsequent drop in morning protein levels near the end of the day in turn activates the "evening" genes, creating a continuous 24-hour loop.

The researchers treated Arabidopsis plants with salicylic acid, to disrupt the normal daily fluctuation of reactive oxygen molecules in the plants' cells. They were surprised to find that the plants' circadian clock genes only made more proteins with the same regular rhythm. Using a mathematical model to explain the phenomenon, they found that rather than run fast or slow, plants treated with salicylic acid activated both their "morning" clock genes and their "evening" clock genes more strongly.

The researchers also identified a gene called NPR1 that links the two clocks, allowing them to work together. NPR1 senses changes in the "tick-tock" of the plants' reactive oxygen species clock, and responds by turning up both the "morning" and the "evening" genes in the other clock.

For more details, read the news release at DukeToday.