The PLETHORA homolog in Marchantia polymorphism plays a pivotal role in land plant evolution

To survive in a terrestrial habitat, the ancestor of land plants must make several modifications, including a meristem allowing for three-dimensional growth, root-like structures for water and nutrient uptake, air pore complexes or stomata that permit air exchange while reduce water loss 1-4, and a defense system to cope with oxidative stress 3,4. Although some of these features may have existed in the ancestors of land plants, and some genes regulating their development have been identified 5-7, how these modifications are coordinately developed has been unknown. This study showed that a functional homolog to PLETHORA (PLT), an AP2/ERF family transcription factor well known for its involvement in meristem maintenance in higher plants 8, exists in the model liverwort Marchantia polymorpha, and that this gene was expressed in and functionally required for all the features described above. Our results thus suggest a crucial role for PLT in early land plant evolution.