In an article published in Current Biology , scientists explore how auxin, a plant hormone, travels through the stem of a moss to shape its architecture. In vascular plants, such as most grasses or trees, it has been known for several decades that auxin is actively transported between cells via dedicated molecular pumps. This study reveals that, in the moss Physcomitrium patens, a much simpler auxin diffusion mechanism is sufficient to explain how architecture is formed, underlining the evolutionary originality of this branch of life.
Auxin, the molecular architect of plant form
Plants come in an incredible variety of shapes. Some are tall and slender, others low and highly branched. One of the reasons for this difference lies in the way they organize the growth of their branches. This process is controlled by a hormone called auxin.
Auxin acts like a position marker: it is produced at different points on the plant - at the top and base of the stems and in the branches - and creates zones of inhibition along the stem, i.e. places where the formation of new branches is blocked. The spacing between these zones largely determines the overall shape of the plant.
In vascular plants, auxin is actively circulated by small molecular pumps that direct its transport in a single direction. But in mosses such as Physcomitrium patens, this system appears to be much less important. Genetic studies had already shown that auxin transport by these pumps plays a limited role in the way these plants branch. This raised the question: how do mosses manage to organize their branches so precisely?
Reference
Abitbol-Spangaro J, Cloarec G, Muller A, Hallet S, Boulogne C, Gillet C, Schmidt V, Dobrev PI, Skokan R, Couvreur V, de Keijzer J, Godin C, Coudert Y. Robust branch patterning in moss shoots via symplasmic auxin diffusion. Curr Biol. 2025 Oct 7:S0960-9822(25)01201-1. doi: 10.1016/j.cub.2025.09.031
