New insight into plants’ ‘magic wand’ to make flowers  

24-08-2021

Scientists have found the key as to how plants make flowers. The research, published in Nature Communications, provides an insight into the evolution of flowering plants. 

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It is like a magic wand for plants, capable of making all the different floral organs. This ‘wand’ is the MADS transcription factors, an ancient gene family present before the ancestral split of animals, plants and fungi. Today, humans and funghi have very few of them, but flowering plants can contain a hundred. They are responsible for many functions in the lifecycle of the plant, including flowering.

Three decades ago, scientists switched a MADS domain from humans with a MADS domain from plants and they were surprised to find that the human one also worked in the plant. “This was really puzzling”, explains Chloe Zubieta, CNRS Research Director from the Laboratoire de Physiologie Cellulaire et Vegetale at the CEA Grenoble (CNRS/Univ. Grenoble Alpes/CEA/INRAE UMR 5168), visiting scientist at the ESRF and corresponding author of the paper. “So the community started looking into the structure of these transcription factors and how they function in humans, fungi and plants”, she says.

Throughout the years, researchers have found a lot of information about the human and fungi MADS transcription factors, but unfortunately the plant ones have proven difficult to crystallise. Now, Zubieta and colleagues from Humboldt-Universität zu Berlin, Wageningen University (The Netherlands) and the ESRF have combined structural biology, genome-wide binding studies and plant transgenics to show  the key to the function of MADS transcription factors. They used ID29 beamline at the ESRF to solve the structure.

The DNA binding domain is the same in humans and plants. So how can you have the same DNA binding domain but all these different functions? It was thought that by changing the function of a transcription factor the domain that binds DNA would change, but that didn’t happen in the experiments carried out.

Instead, they found that a small stretch of ~30 amino acids, sitting on top of the domain, does not directly interact with DNA, but it is key to tuning DNA binding and in turn, key to the functional identity of different MADS transcription factors.  Subtle changes on this part modify the function of the MADS and define whether the flower can make petals or stamen or carpels. So plants have taken a transcription factor family found in humans and fungi too and changed a few amino acids resulting in a master regulator for floral organ development. 

“It basically decides what DNA sequence it prefers and what MADS partners it wants to attach itself to. It also determines how far the DNA binding domains are going to be from each other, so it is a really important part of the MADS protein complex”, explains Zubieta.

 “Over the course of evolution, plants have diversified their so-called I domains, resulting in different genes being regulated and different developmental programs being launched. It is an elegant example of how evolution works”, concludes Zubieta.

Reference:

Lai, X., et al, Nat Commun 12, 4760 (2021). https://doi.org/10.1038/s41467-021-24978-w.

Text by Montserrat Capellas Espuny