Light Sensors Help Plants Overcome Deadly Shade

Plants growing in close quarters are constantly competing to absorb the most sunlight and out-grow each other. However, when a plant succeeds in outgrowing another, it ultimately casts a shadow and blocks much-needed sunlight. To escape the impending shade created by rivals, plants are equipped with specialized light sensors that determine whether a nearby plant is robbing the sun or if a cloud is briefly passing overhead. That way, plants can continue to grow according to plan. 

In a recent study, researchers from the Salk Institute examined how plants use such built-in light sensors to assess the quality of shade and detect the depletion of red and blue light, which are the wavelengths absorbed by vegetation and used for growth. Ultimately, researchers found that blue light depletion triggers accelerated plant growth - a means to overcome taller, competing plants, according to a news release.

"With this knowledge and discoveries like it, maybe you could eventually teach a plant to ignore the fact that it's in the shade and put out a lot of biomass anyway," Joanne Chory, senior author and director of Salk's Plant Molecular and Cellular Biology, said in the release.

Researchers focused on light-sensitive sensors known as cryptochromes, which react to reduced blue light by triggering the genes responsible for accelerated cell growth in plants. These blue light sensors are also associated with a plant's circadian rhythm, or biological clock, and are ultimately responsible for telling the plant when to grow and flower. 

For their experiment, researchers placed normal and mutant Arabidopsis (rockcress) plants in a light-controlled room and then limited the amount of blue light they were exposed to. The genetically modified "mutant" plants lacked both cryptochromes and a PIF transcription factor - a type of protein that connects to the DNA so it can control which genes are switched on and off. Generally speaking, PIFs bind to phytochromes – or red light sensors – to switch off growth hormones.

When observing the plants' response to limited blue light, researchers discovered cryptochromes signal to the DNA transcription factors and activate genes completely different than what photoreceptors activate. This suggests plants are able to quickly respond to light changes in their environment. Knowing this, researchers could create modified plants that grow more aggressively, even in crowded or shaded areas.  

"Ultimately, we could help farmers grow crops very close together by changing how plants put out leaves, how fast the leaves grow and at what angles the leaves grow relative to each other and the stem. This will help increase yield in the next few generations of crop plants," Chory added.

Their findings were published in the journal Cell.

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