Genes outside nucleus have disproportionate effect

Oct 31, 2013 Andy Fell
The tiny bit of DNA outside the cell nucleus has a large effect on metabolism. This may impact future treatments for inherited diseases in humans.
Genes outside nucleus have disproportionate effect

Experiments with Arabidopsis plants like this six-week-old could help shape future IVF treatments. (photo: Baohua Li / UC Davis)

New research from the University of California, Davis, shows that the tiny proportion of a cell’s DNA that is located outside the cell nucleus has a disproportionately large effect on a cell’s metabolism. The work, with the model plant Arabidopsis, may have implications for future treatments for inherited diseases in humans.

Plant and animal cells carry most of their genes on chromosomes in the nucleus, separated from the rest of the cell. However, they also contain a small number of genes in organelles that lie outside the nucleus. These are the mitochondria, which generate energy for animal and plant cells, and chloroplasts, which carry out photosynthesis in plant cells.

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Dan Kliebenstein, UC Davis.
The influence of genes outside the nucleus was known to an earlier generation of field ecologists and crop breeders, said Dan Kliebenstein, professor in the UC Davis Department of Plant Sciences and Genome Center and senior author on the paper published Oct. 8 in the online journal eLife. This is the first time that the effect has been quantified with a genomic approach, he said.

Bindu Joseph, a postdoctoral researcher in Kliebenstein’s lab, and Kliebenstein studied how variation in 25,000 nuclear genes and 200 organellar genes affected the levels of thousands of individual chemicals, or metabolites, in leaf tissue from 316 individual Arabidopsis plants.

They found that 80 percent of the metabolites measured were directly affected by variation in the organellar genes — about the same proportion that were affected by variation among the much larger number of nuclear genes. There were also indirect effects, where organellar genes regulated the activity of nuclear genes that in turn affected metabolism.

“At first it’s surprising, but at another level you almost expect it,” Kliebenstein said. “These organelles produce energy and sugar for cells, so they are very important.”

Similar effects could also occur in mammalian cells, Kliebenstein said. That has implications for in vitro fertilization therapies aimed at preventing diseases caused by faulty mitochondria being passed from mother to child. The British government recently proposed draft regulations for “three-parent embryos,” created by taking a the nucleus from a fertilized egg and putting it into an egg cell from a third donor with its own set of mitochondria. The technique has so far only been tested in animals.

bindu
Bindu Joseph, UC Davis.

“From what we can see in plants, there might be an issue, but it needs testing,” Kliebenstein said.

Large population surveys that aim to link conditions such as obesity to specific genes should also take more account of organellar genes, he said.

Co-authors on the paper are graduate student Jason Corwin and project scientists Baohua Li and Suzi Atwell. The work was supported by the National Science Foundation.

(This article was written by Andy Fell, UC Davis News Service, October 11, 2013.)

About the College of Agricultural and Environmental Sciences, UC Davis

The College of Agricultural and Environmental Sciences at the University of California, Davis, is the leading college of its kind in the world. Its researchers address critical issues related to agriculture, food, the environment, communities, and human and social sciences through cutting-edge research, top-ranked undergraduate and graduate education, and internationally recognized outreach programs. An overarching goal is to develop solutions for a better world, healthier lives, and an improved standard of living for everyone. www.caes.ucdavis.edu

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