More than a phase – Phase separation and clustering of Auxin Response Factor 2 from Marchantia polymorpha

All organisms consist of cells. Eukaryotes (animals, fungi, plants) have complex cells that are themselves composed of specialized compartments called organelles. Most well-known organelles are surrounded by a membrane, though some organelles such as the nucleolus are not, instead forming by the demixing, or phase separation, of proteins, DNA, and/or RNA. These biomolecules condense into a liquid separate from the rest of the cell, and the resulting structures are therefore also called biomolecular condensates.
Auxin Response Factor 2 (MpARF2), a DNA-binding protein in the common liverwort Marchantia polymorpha, has been seen to form assemblies detectable by microscopy. The question then arises whether these are also condensates forming by phase separation, or another process, and how this affects the protein’s function.
We show that MpARF2 is capable of phase separation under native conditions, and that this is regulated by DNA. However, we also find that MpARF2 forms visible clusters, which might better describe the assemblies seen in plant cells.