Plants inherited ability to sense red light from ancient algae

[Global] The light-sensing molecules that tell plants whether to germinate, when to flower and which direction to grow were inherited millions of years ago from ancient algae, says a new study released in the journal Nature Communications.

Plants ‘see’ the world through light-sensitive proteins in their leaves called photoreceptors. These molecules monitor changes in the direction, intensity, duration and wavelength of light shining on a plant, and send signals that tell plants when to sprout, when to blossom, and how to bend or stretch to avoid being shaded by their neighbors.

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A group of photoreceptor proteins called phytochromes enable plants to detect and absorb light in the red and far-red regions of the light spectrum, the main wavelengths of light that plants use for photosynthesis.

Around two decades ago, biologists discovered that plants weren’t the only living things with phytochromes. They also started uncovering similar genes in tiny green bacteria called cyanobacteria.

Based on the similarities between the phytochrome genes in plants and cyanobacteria, scientists proposed that plants acquired their phytochromes millions of years ago by engulfing cyanobacteria that were living independently.

Instead of digesting them, the plant ancestors supplied a safe home for the cyanobacteria to grow, and the cyanobacteria supplied their light-harvesting machinery to help capture energy from the Sun, until the two grew dependent upon one another and eventually joined together to become permanent partners.

The idea is a widely accepted explanation for the origin of chloroplasts, the organelles in plant cells that convert sunlight to food.

But in more recent years researchers have also discovered phytochrome genes in bacteria, fungi and some algae, which got them thinking again: “where did plant phytochromes come from?”

To find out, a group of biologists from the United States, Canada, Europe, and China scoured existing databases and analyzed 300 DNA and RNA sequences from the phytochrome proteins of a wide range of algae and land plants, including ferns, mosses, liverworts, hornworts, green algae, red algae, kelp, diatoms and other green blobs commonly found in ocean plankton.

By calculating the similarities between the sequences, they were able to reconstruct the genetic changes that these red light sensors underwent as they were passed from one lineage to the next.

Plant phytochromes turned out to be more closely related to algae than cyanobacteria, consistent with suspicions that earlier ideas about their bacterial origins may not be right after all.

The researchers also found a surprisingly diverse array of phytochromes in green algae, which could help scientists better understand how plants transitioned from life in the water to life on land.

The diversity of phytochromes in green algae suggests that the aquatic and semi-aquatic ancestors of early plants could absorb and use wavelengths of light that modern land plants can’t ‘see.’

“The first ancestral algae to move onto land would have faced a very different light environment than they experienced in the water – a lot more light, and in different wavelengths. Photoreceptors played a key role in helping plants adapt to these changing light conditions,” said study lead author Dr Li Fay-Wei of Duke University.

 

View original article at: Plants Inherited Ability to Sense Red Light from Ancient Algae

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