Navigation Links
Amoeba may offer key clue to photosynthetic evolution

Stanford, CA -- 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."

Contact: Eva Nowack
Carnegie Institution

Related biology news :

1. Human cells exhibit foraging behavior like amoebae and bacteria
2. Indigenous peoples at forefront of climate change offer lessons on plant biodiversity
3. Superbugs from space offer new source of power
4. Stem cell study in mice offers hope for treating heart attack patients
5. Padded headgear, boxing gloves may offer some protection for fighters
6. A bugs (sex) life: Diving beetles offer unexpected clues about sexual selection
7. Test and Treat model offers new strategy for eliminating malaria
8. Lungs clothed in fresh cells offer new hope for transplant patients
9. Maker of VSL#3 probiotic offers assistance program for ulcerative colitis and ileal pouch patients
10. Metadynamics technique offers insight into mineral growth and dissolution
11. SpringerLink now offers more than 50,000 eBooks
Post Your Comments:
(Date:11/4/2015)... 2015 --> ... by Transparency Market Research "Home Security Solutions Market - Global ... - 2022", the global home security solutions market is expected to ... The market is estimated to expand at a CAGR ... 2022. Rising security needs among customers at homes, the ...
(Date:10/29/2015)... , Oct. 29, 2015  Rubicon Genomics, ... for U.S. distribution of its DNA library preparation ... and Rubicon,s new ThruPLEX Plasma-seq kit. ThruPLEX Plasma-seq ... the preparation of NGS libraries for liquid biopsies--the ... diagnostic and prognostic applications in cancer and other ...
(Date:10/27/2015)... 27, 2015 Munich, Germany ... Mapping technology (ASGM) automatically maps data from mobile eye ... , so that they can be quantitatively analyzed ... Munich, Germany , October 28-29, 2015. SMI,s ... from mobile eye tracking videos created with SMI,s ...
Breaking Biology News(10 mins):
(Date:11/24/2015)... ... November 24, 2015 , ... InSphero AG, the leading supplier ... models, has promoted Melanie Aregger to serve as Chief Operating Officer. , ... the management team and was promoted to Head of InSphero Diagnostics in ...
(Date:11/24/2015)... 2015 /CNW Telbec/ - ProMetic Life Sciences Inc. (TSX: PLI) ... Pierre Laurin , President and Chief Executive Officer of ... Piper Jaffray 27 th Annual Healthcare Conference to be ... 2015. st , at 8.50am (ET) and ... the day. The presentation will be available live via a ...
(Date:11/24/2015)... , Nov. 24, 2015 HemoShear ... on discovering drugs for metabolic disorders, announced today ... to its Board of Directors (BOD). Mr. Watkins ... of Human Genome Sciences (HGS), and also served ... Jim Powers , Chairman and CEO ...
(Date:11/24/2015)... YORK , November 24, 2015 ... in a European healthcare ... which the companies will work closely together in identifying European ... unmet medical need. The collaboration is underpinned by a significant ... fund. This is the first investment by Bristol-Myers Squibb in ...
Breaking Biology Technology: