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. 2019 Jul 19;10:3206. doi: 10.1038/s41467-019-11286-7

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© The Author(s) 2019

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 6 — Evolutionary model for occurrences of furostanol and spirostanol biosynthesis in plants. Through independent gene duplication events followed by neofunctionalization, the latent sterol 16,22-polyhydroxylase activity contained within the ancestral brassinosteroid (BR)-biosynthetic CYP90Bs was recruited to yield 16,22-polyoxygenated cholesterols, which were further derivatized by additionally recruited enzymes to establish the evolutionarily new furostanol- and spirostanol-type steroid biosynthetic systems in certain plants. Despite their evolutionary origin in phytohormone metabolism, these CYP90s exhibit a total suppression of the ancestral sterol 22-monohydroxylase activity likely owing to negative selection, which allow them to fully excise defense function without disturbing BR homeostasis