Ancient cell patterning mechanism for antiherbivore defence discovered in early land plants

Clues from 400-million-year-old fossils reveal how plants first organised specialised defence cells

In a new study published now in Development, scientists show that a process known as lateral inhibition governs how specialized cells are spaced in liverworts, one of the oldest lineages of land plants. By combining fossil analysis, comparative biology and mathematical modelling, the international team led by Josep Mercadal, a postdoc in the group of Pau Formosa-Jordan at the Max Planck Institute for Plant Breeding Research in Cologne, demonstrates that this mechanism is not only present in living species but was already at work over 400 million years ago.
 

Lateral inhibition is a widely used developmental strategy in which cells communicate with their immediate neighbours to prevent them from adopting the same identity. This interaction often leads to regularly spaced patterns of distinct cell types, a principle found across many organisms.

The team identified an ancient mechanism that controls how oil body cells - specialised structures involved in defence against herbivores - are patterned in liverworts. These cells were analysed in both living species and in exceptionally well-preserved fossils of one of the earliest known liverworts, Metzgeriothallus sharonae, in which they are referred to as dark cells. The researchers found that these dark cells are arranged in regular, evenly spaced patterns characteristic of lateral inhibition, revealing that this patterning mechanism was already in place in some of the earliest land plants.

Fossils rarely preserve genetic or molecular information, therefore the evolutionary origins of the mechanisms that control how plant cells acquire their identity have remained difficult to trace.

The authors address this challenge by using computational models to reconstruct the spatial patterns observed in the fossil tissues. They showed that these patterns can be explained by a simple mechanism combining local activation with inhibitory signals between neighbouring cells – which can generate the characteristic regular arrangement of different cell types.

The same principle also accounts for the distribution of oil body cells in modern liverworts such as Marchantia polymorpha.

The study indicates that preserved cellular patterns in fossils can be used to infer ancient developmental mechanisms, providing a new approach to investigating the evolution and conservation of cell specification over hundreds of millions of years.

“These findings suggest that lateral inhibition is a deeply conserved mechanism that has guided cell differentiation in plants since the earliest stages of land plant evolution, highlighting its importance for antiherbivore defence. The work highlights how combining fossil evidence with modern modelling techniques can reveal the origins of fundamental developmental processes.” Josep Mercadal