Featured Research

from universities, journals, and other organizations

Amoeba may offer key clue to photosynthetic evolution

Date:
February 27, 2012
Source:
Carnegie Institution
Summary:
The major difference between plant and animal cells is the photosynthetic process, which converts light energy into chemical energy. When light isn't available, energy is generated by breaking down carbohydrates and sugars, just as it is in animal and some bacterial cells. Two cellular organelles are responsible for these two processes: the chloroplasts for and the mitochondria. New research has opened a window into the early stages of chloroplast evolution.

Paulinella chromatophora as viewed through a light (top) and electron (bottom) microscope. Cr, chromatophore; G, golgi; M, mitochondrion; N, nucleus; T, theca (cell wall composed of silica scales).
Credit: Image courtesy of Eva Nowack, PhD, Department of Plant Biology, The Carnegie Institution for Science

The major difference between plant and animal cells is the photosynthetic process, which converts light energy into chemical energy. When light isn't available, energy is generated by breaking down carbohydrates and sugars, just as it is in animal and some bacterial cells. Two cellular organelles are responsible for these two processes: the chloroplasts for photosynthesis and the mitochondria for sugar breakdown. New research from Carnegie's Eva Nowack and Arthur Grossman has opened a window into the early stages of chloroplast evolution.

Their work is published online by the Proceedings of the National Academy of Sciences in the week of February 27-March 2.

It is widely accepted that chloroplasts originated from photosynthetic, single-celled bacteria called cyanobacteria, which were engulfed by a more complex, non-photosynthetic cell more than 1.5 billion years ago. While the relationship between the two organisms was originally symbiotic, over evolutionary time the cyanobacterium transferred most of its genetic information to the nucleus of the host organism, transforming the original cyanobacterium into a chloroplast that is no longer able to survive without its host. A similar process resulted in the creation of mitochondria.

To sustain the function of the organelle, proteins encoded by the transferred genes are synthesized in the cytoplasm, or cell's interior, and then imported back into the organelle. In most systems that have been studied, the transport of proteins into the chloroplast occurs through a multi-protein import complex that enables the proteins to pass through the envelope membranes that surround the chloroplast.

Clearly the events that gave rise to chloroplasts and mitochondria changed the world forever. But it is difficult to research the process by which this happened because it took place so long ago. One strategy used to elucidate the way in which this process evolved has relied on identifying organisms for which the events that resulted in the conversion of a bacterium into a host-dependent organelle occurred more recently.

Nowack and Grossman focused their research on a type of amoeba called Paulinella chromatophora, which contains two photosynthetic compartments that also originated from an endosymbiotic cyanobacterium, but that represent an earlier stage in the formation of a fully evolved organelle.

These compartments, called chromatophores, transferred more than 30 of the original cyanobacterial genes to the nucleus of the host organism. While gene transfer has been observed for other bacterial endosymbionts, the function of the transferred genes has been unclear, since it does not appear that the endosymbionts (in contrast to organelles) are equipped to recapture those proteins, because they do not have appropriate protein import machineries.

The Carnegie team honed in on three of the P. chromatophora transferred genes, which encode proteins involved in photosynthesis, a process localized to the chromatophore. They set out to determine whether these proteins are synthesized in the cytoplasm of the amoeba and whether the mature proteins became localized to the chromatophore.

Using an advanced array of research techniques, they were able to determine that these three proteins are synthesized in the cytoplasm and then transported into chromatophores, where they assemble together with other, internally encoded proteins into working protein complexes that are part of the photosynthetic process.

Interestingly, the process by which these proteins are transported into chromatophores may also be novel and involve transit through an organelle called the Golgi apparatus, prior to becoming localized to the chromatophore. This suggests the occurrence of an initial, rudimentary process for proteins to cross the envelope membrane of the nascent chloroplast. This process ultimately evolved into one that is potentially more sophisticated and that uses specific protein complexes for efficient transport.

"This work demonstrates that P. chromatophora is a potentially powerful model for studying evolutionary processes by which organelles developed," Nowack said. "Obtaining a comprehensive list of proteins imported into chromatophores, including their functions and origins, as well as understanding the pathway by which these proteins are imported, could provide insight into the mechanism that eukaryotic cells use to 'enslave' bacteria and turn them into organelles such as chloroplasts and mitochondria."

This research was supported by Michael Melkonian, Deutsche Forschungsgemeinschaft, and the National Science Foundation.

The Carnegie Institution for Science (carnegiescience.edu) is a private, nonprofit organization headquartered in Washington, D.C., with six research departments throughout the U.S. Since its founding in 1902, the Carnegie Institution has been a pioneering force in basic scientific research. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.


Story Source:

The above story is based on materials provided by Carnegie Institution. Note: Materials may be edited for content and length.


Journal Reference:

  1. Eva C. M. Nowack and Arthur R. Grossman. Trafficking of protein into the recently established photosynthetic organelles of Paulinella chromatophora. Proceedings of the National Academy of Sciences, February 27, 2012 DOI: 10.1073/pnas.1118800109

Cite This Page:

Carnegie Institution. "Amoeba may offer key clue to photosynthetic evolution." ScienceDaily. ScienceDaily, 27 February 2012. <www.sciencedaily.com/releases/2012/02/120227152819.htm>.
Carnegie Institution. (2012, February 27). Amoeba may offer key clue to photosynthetic evolution. ScienceDaily. Retrieved October 22, 2014 from www.sciencedaily.com/releases/2012/02/120227152819.htm
Carnegie Institution. "Amoeba may offer key clue to photosynthetic evolution." ScienceDaily. www.sciencedaily.com/releases/2012/02/120227152819.htm (accessed October 22, 2014).

Share This



More Plants & Animals News

Wednesday, October 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Working Mother DIY: Pumpkin Pom-Pom

Working Mother DIY: Pumpkin Pom-Pom

Working Mother (Oct. 22, 2014) How to make a pumpkin pom-pom. Video provided by Working Mother
Powered by NewsLook.com
San Diego Zoo's White Rhinos Provide Hope for the Critically Endangered Species

San Diego Zoo's White Rhinos Provide Hope for the Critically Endangered Species

Reuters - Light News Video Online (Oct. 22, 2014) The pair of rare white northern rhinos bring hope for their species as only six remain in the world. Elly Park reports. Video provided by Reuters
Powered by NewsLook.com
Raw: Bear Cub Strolls Through Oregon Drug Store

Raw: Bear Cub Strolls Through Oregon Drug Store

AP (Oct. 22, 2014) Shoppers at an Oregon drug store were surprised by a bear cub scurrying down the aisles this past weekend. (Oct. 22) Video provided by AP
Powered by NewsLook.com
Family Pleads for Pet Pig to Stay at Home

Family Pleads for Pet Pig to Stay at Home

AP (Oct. 22, 2014) The Johnson family lost their battle with the Chesterfield County, Virginia Planning Commission to allow Tucker, their pet pig, to stay in their home, but refuse to let the board keep Tucker away. (Oct. 22) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins