Plants form new leaves, flowers and roots at the tips of shoots and roots, in specific growth regions known as meristems. These meristems contain stem cells that divide as needed and form new cells that develop into specialised tissue. Using the example of plant roots, researchers from Freiburg have now been able to decipher which regulatory mechanisms ensure that growth in the meristem occurs in a controlled manner. The results have been published in the journal Nature Plants.
Stem cells are dependent on signals from other cells
The fact that stem cells can continuously divide and form progenitor cells for specialised tissues is not a matter of course: signals from other cells are necessary to control the properties of stem cells. This dependence on signalling processes is also a protective mechanism. If stem cells were able to multiply uncontrollably, this would lead to uncontrolled growth, as in the case of cancer.
WOX5 is an important signalling molecule that regulates stem cells in the meristem. However, the mechanism through which it does this was previously unknown. A research team led by Prof. Dr. Thomas Laux, a member of the CIBSS – Centre for Integrative Biological Signalling Studies Cluster of Excellence at the University of Freiburg, has now succeeded in decoding this mechanism. The team identified HAN as an essential factor that transmits the function of WOX5.
The gene-regulating molecule HAN is an important regulator for plant growth.
"We were able to show that HAN transmits the WOX5 signal and ensures that the CDF4 gene remains inactive in stem cells," explains Laux. "CDF4 would otherwise cause stem cell properties to be inhibited. By suppressing CDF4, HAN allows the stem cells in the root meristem to remain undifferentiated and continue dividing."
The team used molecular biology methods as well as mathematical modelling. These provide a possible explanation as to why the seemingly complicated mechanism could be an advantage for the plant: the involvement of HAN as a link between WOX5 and CDF4 appears to make the regulation of stem cells less sensitive to environmental influences. "In further investigations, we now want to find out whether the multi-level nature of the process actually has the effect that we see in the modelling," says Laux.
Process also important for plant breeding
A precise understanding of the processes by which plants grow is an important basis for breeding more resilient or higher-yielding crops. This is because it allows the targeted identification and selection of plants that can grow and produce yields even under less-than-ideal conditions, such as extreme weather.
