Bona Fide Plant Steroid Receptors are Innovated in Seed Plants and Angiosperms through Successive Whole-Genome Duplication Events.

This article focuses on the evolutionary origin and diversification of brassinosteroid (BR) receptors and biosynthetic enzymes in land plants, emphasizing the role of whole-genome duplication (WGD) events. It demonstrates that the orphan BR receptor BRL2 first appeared in stomatophytes (land plants with stomata), while active BR receptors BRL1/3 and the essential receptor BRI1 originated in seed plants and angiosperms, respectively, coinciding with ζ-WGD and ɛ-WGD events. The study reveals that BR biosynthetic enzymes CYP90 are present across all land plants, whereas CYP85A, responsible for producing bioactive BRs, emerged in seed plants alongside BRL1/3. Sequence and expression analyses indicate that BR receptors underwent neofunctionalization through adaptive divergence, particularly in their hormone-binding island domains (IDs), with BRI1 showing the highest diversification and expression in angiosperms. These findings suggest that WGDs facilitated the innovation and functional specialization of BR signaling components, potentially contributing to the evolutionary success and ecological dominance of seed plants and flowering plants.