A liverwort view of gibberellin biosynthesis

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Sun et al. investigated genes related to gibberellin biosynthesis in the liverwort Marchantia polymorpha and found them to be critical for far-red light responses. The Plant Cell (2023). 

https://doi.org/10.1093/plcell/koad216

By Rui Sun and Takayuki Kohchi (Kyoto University)

Background: The emergence and diversification of plant hormones over the past 450 million years is a fascinating part of land plant evolution. Gibberellins are a group of plant hormones that promote growth and regulate many developmental processes in flowering plants, and the gibberellin biosynthesis pathway is conserved in vascular plants including ferns and lycophytes. The sister lineage of vascular plants, bryophytes, lacks the ability to produce canonical gibberellins but encodes early-step enzymes for producing gibberellin precursors. It is possible that genes for these enzymes are inherited from the common ancestor of all land plants, but their physiological roles are less clear in bryophytes, especially in the liverwort and hornwort lineages.

Question: Are gibberellin precursors used to synthesize plant hormones in liverworts? What is the physiological activity of this putative hormone?

Findings: By chemical analysis, we detected a gibberellin (GA) biosynthesis intermediate, GA12, in the liverwort Marchantia polymorpha, but no canonical bioactive gibberellins. Genetic mutants and enzymatic assays nailed down the major enzymes for the production of GA12 and its precursor, ent-kaurenoic acid. We hypothesize that both substrates are involved in the biosynthesis of an unknown gibberellin-related hormone, GAMp. Far-red enriched light, which indicates the presence of competitive neighbors in nature, promotes GA12 accumulation in M. polymorpha. The biosynthesis enzymes are also indispensable for the liverwort to carry out proper developmental responses, including changes in growth direction and acceleration of sexual reproduction. Interestingly, overall plant growth is enhanced in GAMp-deficient mutants, which is opposite to gibberellin deficiency phenotypes in flowering plants.

Next steps: We hope to find the exact chemical structure and the complete biosynthetic route of GAMp. Since the canonical gibberellin receptor is not conserved in bryophytes, we are also curious about how GAMp is perceived.

Reference: 

Rui Sun, Maiko Okabe, Sho Miyazaki, Toshiaki Ishida, Kiyoshi Mashiguchi, Keisuke Inoue, Yoshihiro Yoshitake, Shohei Yamaoka, Ryuichi Nishihama, Hiroshi Kawaide, Masatoshi Nakajima, Shinjiro Yamaguchi, Takayuki Kohchi. (2023). Biosynthesis of gibberellin-related compounds modulates far-red light responses in the liverwort Marchantia polymorpha. https://doi.org/10.1093/plcell/koad216

苔类植物为赤霉素生物合成提供新视野

最近，来自日本京都大学的孙芮等人在The Plant Cell在线发表了题为Biosynthesis of gibberellin-related compounds modulates far-red light responses in the liverwort Marchantia polymorpha的研究论文，探索了苔类植物地钱中的赤霉素合成相关基因及其生理功能。

01 背景回顾：

在陆地植物长达4.5亿年的演化历史中，植物激素的起源和多样性分化是不可或缺的一环。在被子植物中，赤霉素是一类重要的植物激素，调节多种生长发育过程。此前研究认为，赤霉素的完整合成通路在包括蕨类和小叶类植物在内的维管植物中是保守的；而维管植物的姐妹类群——苔藓植物中缺乏关键合成酶，无法通过经典途径产生有生理活性的赤霉素。然而，赤霉素合成途径中催化前期步骤的多种合成酶在苔藓植物的基因组里普遍存在，意味着它们可能继承自陆地植物的共同祖先。在苔藓植物特别是苔类和角苔类植物中，对这些酶的生理作用研究还相当有限。

02 科学问题

苔类植物是否利用部分赤霉素合成通路来产生植物激素？该通路可能的生理功能是什么？

03 研究发现

通过质谱分析，我们检测了苔类植物地钱（Marchantia polymorpha）中的赤霉素相关化合物，除合成中间体GA12外未检出其他常见赤霉素。利用遗传和生化分析，我们确定了地钱中GA12及其前体对映-贝壳杉烯酸（KA）的主要合成酶（即MpCPS、MpKS、MpKOL1和MpKAOL1），并提出KA和GA12可能参与合成一种未知的类赤霉素激素GAMp。在自然环境下，周围植物的竞争会造成光照中远红光组分的增加。实验条件下远红光富集会促使地钱提高GA12的积累，而缺乏赤霉素相关合成酶的地钱则无法完成对远红光的发育响应，既无法改变生长极性也无法快速进入有性生殖。有趣的是，在地钱中阻断GAMp的合成常常促进植物生长，跟被子植物中赤霉素缺乏造成的矮小表型截然相反。

04 展望未来

我们将继续探索GAMp的活性形式和完整合成途径。鉴于苔藓植物同样缺失被子植物中的经典赤霉素受体GID1，我们也希望了解GAMp的信号感受机制。

原文作者：Rui Sun et al.

翻译：Rui Sun, Haonan Bao (Kyoto University)