It is said that more than 300,000 species of terrestrial plants inhabit the earth, and that terrestrial plants account for about 80% of the biomass (weight of living organisms) on the earth. In addition to flowering angiosperms, terrestrial plants include gymnosperms such as cedar and pine, ferns and pinnipeds, which reproduce by spores rather than seeds, and mosses, which do not have vascular bundles. Recent molecular phylogenetic analysis has shown that all living land plants are derived from a single common ancestor that diverged from green algae about 500 million years ago. So what kind of organism was the common ancestor of land plants? Unfortunately, there is no direct way to answer this question, as no fossils have yet been discovered that would allow us to determine what plants looked like at that time.

In angiosperms, auxin regulates development and growth throughout the life cycle, including organogenesis of roots, leaves, and flowers, vascular patterning, and bending response to light and gravity, and is widely used in agriculture as a herbicide and root promoter. Most of the plants used in agriculture and other industrial applications are angiosperms, and most of the auxin research in the past has been conducted on angiosperms. The results of these studies revealed that the auxin response is mainly mediated by the ARF protein, but the large number of genes involved in the auxin response in angiosperms (e.g., rice has 25 different ARF genes) has hindered research. The evolutionary question of when and how the auxin response mechanism was acquired is also an unresolved issue. The evolutionary question of how and when the auxin response mechanism was acquired remained unresolved. In 2008, we began our research using the Zeni moss (Fig. 1), which was being developed as a new experimental model at the time. In addition to its advantages such as fast growth, easy cultivation, and high efficiency of genetic recombination, preliminary analysis suggested that it had low genetic redundancy, and we thought it would be useful as a new model for auxin research.

Currently, I am working on several research themes in parallel based on my previous auxin research using Zeni mosses, one of which is the analysis of auxin-responsive genes common to land plants discovered through comparative analysis of mosses and ferns. The auxin response mechanism itself is nothing more than a switch that activates a specific group of genes, and I would like to understand the mechanism that changes the shape and physical and chemical properties of cells beyond the switch. Another theme is to understand the mechanism of formation of goblet bodies and asexual buds (Fig. 4), which are organs for asexual reproduction. These organs are unique to A. zeama and related species, but recent studies have shown that hormones common to land plants, including auxin, are involved in their regulation, and we expect that this will lead to the elucidation of the developmental control mechanisms common to land plants. We also believe that model organisms, including Zeni mosses, are specialized organisms that have evolved in the same way as other species, and that experiments using more plant species are needed to understand common principles. In the future, we would like to conduct experiments using small-leaved plants and ferns, which are divided between mosses and angiosperms.