Featured Research

from universities, journals, and other organizations

It's not easy being green: Scientists grow understanding of how photosynthesis is regulated

Date:
May 19, 2011
Source:
Salk Institute
Summary:
The seeds sprouting in your spring garden may still be struggling to reach the sun. If so, they are consuming a finite energy pack contained within each seed. Once those resources are depleted, the plant cell nucleus must be ready to switch on a "green" photosynthetic program. Researchers recently showed a new way that those signals are relayed.

Once the energy resources in a seed are depleted, seedlings switch on a "green" photosynthesis program (Arabidopsis seedling at the top).
Credit: Courtesy of Jesse Woodson, Salk Institute for Biological Studies

The seeds sprouting in your spring garden may still be struggling to reach the sun. If so, they are consuming a finite energy pack contained within each seed. Once those resources are depleted, the plant cell nucleus must be ready to switch on a "green" photosynthetic program. Researchers at the Salk Institute for Biological Studies recently showed a new way that those signals are relayed.

Related Articles


In a study published in the May 24, 2011, issue of the journal Current Biology, a team led by Joanne Chory, Ph.D., professor and director of the Plant Molecular and Cellular Biology Laboratory, and including postdoctoral fellows, Jesse Woodson, Ph.D., and Juan Perez-Ruiz, Ph.D., identify a signaling factor sent by plant chloroplasts to turn on photosynthesis-related genes. Their finding may help achieve greater crop yields and better plant health.

"When a seedling establishes a photosynthetic lifestyle, it needs to activate several thousand genes in the nucleus," says Chory, also a Howard Hughes Medical Institute investigator and holder of the Howard H. and Maryam R. Newman Chair in Plant Biology. "One of the signals to do this comes from the organelle in charge of photosynthesis, called the chloroplast. In this study we identified this signaling molecule as heme."

Although in plants and animals most genes reside in the nucleus, small DNA rings of genes are found in other cellular venues such as energy-producing mitochondria. Plant chloroplasts, whose primary function is to turn light and carbon dioxide into energy and carbohydrates required for growth, also contain genes that regulate photosynthesis-related factors encoded in the plant cell nucleus.

"The Chory lab previously identified mutations in five genes in Arabidopsis thaliana plants that were unable to synthesize molecules such as chlorophyll or respond to signals generated by intermediates of the chlorophyll biosynthetic pathway," explains Woodson, the study's first author. "Those studies suggested that when plants undergo stress, an intermediate accumulates that tells the nucleus to stop 'turning green.'"

These mutants -- called GUN (for genomes uncoupled) 1 to 5 -- lack proteins necessary to relay these signals to the nucleus. Chloroplasts in normal plants might deploy those signals when plants encounter stress, such as too much heat or too little water. Inhibitory signals could also be sent when germinating sprouts are not yet mature enough to make the leap from relying on the seed energy pack to generating their own energy using sunlight.

Suspecting that positive signals must also govern the process, the team screened Arabidopsis for factors that switched photosynthetic proteins on, rather than off. For that, they employed an experimental approach called activation tagging, in which gene-activating DNA sequences are inserted randomly into the Arabidopsis genome and plants are then subjected to a herbicide shower. The team then looked for any survivor that persisted in making photosynthetic proteins. By definition, in that mutant plant a gene required to sustain a photosynthetic growth response must have been experimentally switched on.

What they found was a gene designated gun 6, which encodes the enzyme ferrochelatase 1 (FC1), the first gun mutant indicating a positive rather than a negative signal. "Gun 6 mutants make too much FC1 protein, an enzyme required to make a signaling molecule called heme," explains Woodson. Although it is a cofactor in numerous plant and animal pathways, heme is most famous as the oxygen-carrying component of hemoglobin.

The study suggests that excess heme drives expression of photosynthesis-related genes. "If a plant makes abnormally high levels of heme, the nucleus could be unaware that the chloroplast is nonfunctional and may keep making growth-related proteins," says Woodson. "Heme is likely the signal sent from a healthy chloroplast to the nucleus saying it is time to make proteins required for photosynthesis."

The team also genetically engineered plants to make too much of an FC1 isoform, known as FC2, and found photosynthesis-related genes were not upregulated, suggesting that heme made from FC2 differs from that made by FC1, and that overall signals regulating plant growth are highly complex.

The mustard plant Arabidopsis is favored by plant biologists for the same reasons that animal biologists rely on mice and fruitflies -- it's easy to grow, compact, reproduces rapidly (which for plant biologists means it makes tons of seeds -- and fast), its genome is sequenced, and it can be manipulated genetically.

Plus, it is incredibly boring. "There is nothing unusual about Arabidopsis," notes Woodson. "Which is good, because anything we learn from it will be generally true for most plants."

Affirming that "every plant" quality, the team isolated the corn (Zea mays) equivalent of the FC1 gene and engineered Arabidopsis to make artificially high levels of the corn protein. Like gun 6 mutants, those plants continued to make photosynthesis-related genes when subjected to herbicide, demonstrating that FC1 likely does the same thing in a crop plant as it does in a weed. However, analysis of corn, rice or barley would be experimentally less practical, given their longer growth cycles and the space required to grow them.

"Overall, this work answers basic questions regarding how a plant grows, builds chloroplasts and harvests light energy in order to turn into a photosynthetic organism," says Chory. "Understanding how plants coordinate gene expression between the chloroplast and nucleus will ultimately increase crop yields in the field, where plants often encounter multiple stresses during the growing season."

The work was supported by the Department of Energy and the Howard Hughes Medical Institute. Jesse Woodson and Juan Perez-Ruiz had postdoctoral fellowships from the National Institutes of Health and the Spanish Ministry of Education.


Story Source:

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


Journal Reference:

  1. Jesse D. Woodson, Juan M. Perez-Ruiz, and Joanne Chory. Heme Synthesis by Plastid Ferrochelatase I Regulates Nuclear Gene Expression in Plants. Current Biology, 2011; DOI: 10.1016/j.cub.2011.04.004

Cite This Page:

Salk Institute. "It's not easy being green: Scientists grow understanding of how photosynthesis is regulated." ScienceDaily. ScienceDaily, 19 May 2011. <www.sciencedaily.com/releases/2011/05/110518092046.htm>.
Salk Institute. (2011, May 19). It's not easy being green: Scientists grow understanding of how photosynthesis is regulated. ScienceDaily. Retrieved December 20, 2014 from www.sciencedaily.com/releases/2011/05/110518092046.htm
Salk Institute. "It's not easy being green: Scientists grow understanding of how photosynthesis is regulated." ScienceDaily. www.sciencedaily.com/releases/2011/05/110518092046.htm (accessed December 20, 2014).

Share This


More From ScienceDaily



More Plants & Animals News

Saturday, December 20, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Researchers Test Colombian Village With High Alzheimer's Rates

Researchers Test Colombian Village With High Alzheimer's Rates

AFP (Dec. 19, 2014) In Yarumal, a village in N. Colombia, Alzheimer's has ravaged a disproportionately large number of families. A genetic "curse" that may pave the way for research on how to treat the disease that claims a new victim every four seconds. Duration: 02:42 Video provided by AFP
Powered by NewsLook.com
Monarch Butterflies Descend Upon Mexican Forest During Annual Migration

Monarch Butterflies Descend Upon Mexican Forest During Annual Migration

Reuters - Light News Video Online (Dec. 19, 2014) Millions of monarch butterflies begin to descend onto Mexico as part of their annual migration south. Rough Cut (no reporter narration) Video provided by Reuters
Powered by NewsLook.com
Birds Might Be Better Meteorologists Than Us

Birds Might Be Better Meteorologists Than Us

Newsy (Dec. 19, 2014) A new study suggests a certain type of bird was able to sense a tornado outbreak that moved through the U.S. a day before it hit. Video provided by Newsy
Powered by NewsLook.com
Navy Unveils Robot Fish

Navy Unveils Robot Fish

Reuters - Light News Video Online (Dec. 18, 2014) The U.S. Navy unveils an underwater device that mimics the movement of a fish. Tara Cleary reports. Video provided by Reuters
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