Max Planck researchers make a breakthrough in plant stem cell research

December 22, 2005

Totipotent stem cells allow plants to build new organs throughout their whole life. But it has been unclear how hormones and genetic factors work together to prevent plants from having growth that is either stunted, or uncontrolled and tumor-like. Scientists from the Max Planck Institute for Developmental Biology have now uncovered a feedback mechanism, involving a growth-enhancing hormone and a regulatory protein, which controls the number of stem cells the plant produces. (Nature, December 22, 2005). The results are of great importance for all of stem cell research.

All above ground parts of a plant - leaves, stem, flowers, and seeds - ultimately are derived from cells of a small tissue at the tip of the shoot. Biologists call this tissue the "apical meristem", and it contains totipotent stem cells that are active throughout the life of the plant. Unlike the stem cells of animals, which can only produce specific kinds of tissue after the animal is past its embryonic stage, plant stem cells remain their totipotency and, therefore plants can continue growing over many years, developing new organs.

But this ability comes at a price. If the number of meristematic stem cells increases too quickly, then there could be uncontrolled growth, similar to cancer. On the other hand, if the stem cell pool shrinks too quickly, the plant could have stunted growth. In order to stay alive and reproduce, the plant needs to find the right balance in the number of its stem cells. Two regulatory mechanisms were found to be important for this process. The first involves growth-promoting hormones like auxin and cytokinin, known already for more than half a century. The second involves genetic factors, which were discovered at the University of Tübingen, Germany about a decade ago. Here it was shown that a gene called WUSCHEL has a key influence on how many cells in the apical meristem actually stay stem cells. However, until now, it was unclear how hormones and regulatory genes, such as WUSCHEL work together to maintain this fine balance at the tip of the shoot.

The working group led by Dr. Jan Lohmann at the Max Planck Institute for Developmental Biology in Tübingen, Germany has now solved this problem. The object of investigation was Arabidopsis thaliana, the "favorite plant" for molecular and genetic research, whose genome was sequenced years ago. Lohmannâ€TMs team now carried out elaborate genetic and biochemical experimentation, and thereby identified four genes, which might serve as a mechanistic connection between plant hormones and the genetic regulatory elements in meristem.

The researchers in Tübingen used gene expression analysis to show that the genes ARR5, ARR6, ARR7 and ARR 15, "Arabidopsis Response Regulators", are subject to genetic regulation via the WUSCHEL gene. In particular, WUSCHEL restricts the activity of ARR7 in the apical meristem. The ARR genes in turn carry out a particularly important task in hormonal regulation: they are part of a negative feedback loop, by which the growth-inducing plant hormone cytokinin limits its own influence. The study shows that the ARR genes play a direct role in regulation of the stem cell pool.

The hormone itself instigates the meristematic stem cells to split; at the same time, it activates various ARR genes, which break the cytokinin signal chain. Jan Lohmann explains that "WUSCHEL supports the cytokinin effect by stopping its negative feedback." That is also the reason for earlier observations, that Arabidopsis samples with defective WUSCHEL genes only develop very small meristems, and have trouble growing. The researchers in Tübingen have now discovered the same effect in mutants whose ARR7 gene is constitutively active.

Cytokinin can only have its full growth-promoting effect in tissue in which the WUSCHEL regulatory gene is active. "Meristematic regulation is a fabulous example of how the effects of free circulating hormones can be limited to a particular tissue," Lohmann says. Only with this kind of mechanism, is it possible that the same hormone has different effects in different tissues, depending on which genetic conditions it encounters.
-end-
Original work:
Andrea Leibfried, Jennifer P. C. To, Wolfgang Busch, Sandra Stehling, Andreas Kehle, Monika Demar, Joseph J. Kieber & Jan U. Lohmann WUSCHEL controls meristem function by direct regulation of cytokinin inducible response regulators
Nature, December 22, 2005

Max-Planck-Gesellschaft

Related Stem Cells Articles from Brightsurf:

SUTD researchers create heart cells from stem cells using 3D printing
SUTD researchers 3D printed a micro-scaled physical device to demonstrate a new level of control in the directed differentiation of stem cells, enhancing the production of cardiomyocytes.

More selective elimination of leukemia stem cells and blood stem cells
Hematopoietic stem cells from a healthy donor can help patients suffering from acute leukemia.

Computer simulations visualize how DNA is recognized to convert cells into stem cells
Researchers of the Hubrecht Institute (KNAW - The Netherlands) and the Max Planck Institute in Münster (Germany) have revealed how an essential protein helps to activate genomic DNA during the conversion of regular adult human cells into stem cells.

First events in stem cells becoming specialized cells needed for organ development
Cell biologists at the University of Toronto shed light on the very first step stem cells go through to turn into the specialized cells that make up organs.

Surprising research result: All immature cells can develop into stem cells
New sensational study conducted at the University of Copenhagen disproves traditional knowledge of stem cell development.

The development of brain stem cells into new nerve cells and why this can lead to cancer
Stem cells are true Jacks-of-all-trades of our bodies, as they can turn into the many different cell types of all organs.

Healthy blood stem cells have as many DNA mutations as leukemic cells
Researchers from the Princess Máxima Center for Pediatric Oncology have shown that the number of mutations in healthy and leukemic blood stem cells does not differ.

New method grows brain cells from stem cells quickly and efficiently
Researchers at Lund University in Sweden have developed a faster method to generate functional brain cells, called astrocytes, from embryonic stem cells.

NUS researchers confine mature cells to turn them into stem cells
Recent research led by Professor G.V. Shivashankar of the Mechanobiology Institute at the National University of Singapore and the FIRC Institute of Molecular Oncology in Italy, has revealed that mature cells can be reprogrammed into re-deployable stem cells without direct genetic modification -- by confining them to a defined geometric space for an extended period of time.

Researchers develop a new method for turning skin cells into pluripotent stem cells
Researchers at the University of Helsinki, Finland, and Karolinska Institutet, Sweden, have for the first time succeeded in converting human skin cells into pluripotent stem cells by activating the cell's own genes.

Read More: Stem Cells News and Stem Cells Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.