The SABATH family enzymes are a group of plant-specific methyltransferases that catalyze the methylation of many small molecules, including several plant hormones. While this family emerged anciently before the evolution of land plants from streptophyte algae, little is known about their biological function in plant lineages other than angiosperms. Here, we identified 12 SABATH family genes from the liverwort Marchantia polymorpha and found that MpSABATH2 plays a critical role in development. Mpsabath2 mutants were severely inhibited in thallus growth and gemma cup formation, while spontaneously forming sexual branches under non-inductive conditions. These phenotypes resembled the developmental responses to far-red light, which was also supported by transcriptome analysis. Further genetic analysis connected this phenomenon with gibberellin (GA)-related metabolism. Blocking GA biosynthesis partially rescued Mpsabath2 phenotypes, which were restored by treatment with the GA precursor, ent-kaurenoic acid. Given that MpSABATH2 belongs to a phylogenetic clade distinct from previously reported phytohormone-methylating SABATH enzymes, our findings suggest that SABATH family enzymes independently acquired roles in developmental regulation through parallel evolution in land plants.
Kawamura et al. (Tue,) studied this question.