Green Stem Cells in a Moss

Israeli-German Research Consortium Discovers Ancient Control Mechanism of Plant Growth

Freiburg, 02.07.2009

From the cover of Development 136.

Although every cell of a living organism contains essentially the same genes, most animals and plants are composed of a huge variety of different cell types with special functions: Humans can’t think with their skin, and roses can’t flower with their roots. An Israeli-German Research Consortium has discovered what makes the difference in a moss.

The process of evolution from bacteria to higher organisms such as humans or roses saw the development of a large amount of different cell types with specific functions. A central question in biology is: “How do different cell types and organs develop from a totipotent fertilized egg?” Though all these cells share the same full set of genes, these are used differently. While whole blocks of genes are shut off in one cell type, in other cells they are turned on. This is realized by protein master switches in a process called “epigenetics” which means “beyond genetics”. One of these master switches is a huge complex of different proteins, the so-called Polycomb (PcG) complex.

The research teams of Dr. Nir Ohad (Tel Aviv University, Israel) and Professor Ralf Reski (Freiburg University, Germany) now report in the latest issue of the renowned scientific journal “Development” (Assaf Mosquna et al. (2009): Development 136, 2433-2444) on the identification of one member from this complex, the FIE protein from the moss Physcomitrella patens. The editors of “Development” were so enthusiastic about the results that they will not only feature this publication in a special editorial (“Plant PcG conservation identiFIEd”) but also advertise the research with a front cover picture.

What did the Israeli-German research consortium, which was well-funded by the German-Israeli Foundation (GIF), discover? The researchers found that the moss FIE gene was active only in moss stem cells, like the egg cell. Furthermore, they found that soon after fertilization of the egg cell, the FIE gene became inactive in the young embryo. In addition, when this gene was inactivated (mutated) by gene technology, moss cells began to proliferate in an uncontrolled manner reminiscent of cancer cells in humans and animals. Much to their surprise, the researchers succeeded in reverting this uncontrolled cell proliferation in the mutant moss by inserting a FIE gene from the seed plant Arabidopsis. “On first sight I could not believe what I saw – I was struck by a gene complementation between organisms that are separated by 450 million years of evolution”, says Nir Ohad. And Ralf Reski adds: “I was fascinated to see cancer-like cell growth in a simple plant like Physcomitrella. This makes moss an excellent model system for studying many fundamental biological questions, even in stem cell research.”

Obviously, these results have not only convinced the reviewers and editors of “Development” but also the reviewers and the Directors of GIF: The latter just granted another proposal of the two teams to continue their joint research on what makes a stem cell in a simple plant.

Legend: Two “uteri” (archegonia) of Physcomitrella. The blue staining reveals expression of the FIE gene in unfertilised egg cells (right). This expression ceases after fertilisation in the young embryo (left). From the cover of Development 136.

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