• Jasmonates are fatty acid-derived hormones that regulate multiple aspects of plant development, growth and stress responses. Bioactive jasmonates, defined as the ligands of the conserved COI1 receptor, differ between vascular plants and bryophytes (jasmonoyl-l-isoleucine (JA-Ile) and dinor-12-oxo-10,15(Z)-phytodienoic acid (dn-OPDA), respectively). The biosynthetic pathways of JA-Ile in the model vascular plant Arabidopsis thaliana have been elucidated. However, the details of dn-OPDA biosynthesis in bryophytes are still unclear.
• Here, we identify an orthologue of Arabidopsis fatty-acid-desaturase 5 (AtFAD5) in the model liverwort Marchantia polymorpha and show that FAD5 function is ancient and conserved between species separated by more than 450 million years (Myr) of independent evolution. Similar to AtFAD5, MpFAD5 is required for the synthesis of 7Z-hexadecenoic acid. Consequently, in Mpfad5 mutants, the hexadecanoid pathway is blocked, dn-OPDA concentrations are almost completely depleted and normal chloroplast development is impaired.
• Our results demonstrate that the main source of wounding-induced dn-OPDA in Marchantia is the hexadecanoid pathway and the contribution of the octadecanoid pathway (i.e. from OPDA) is minimal.
• Remarkably, despite extremely low concentrations of dn-OPDA, MpCOI1-mediated responses to wounding and insect feeding can still be activated in Mpfad5, suggesting that dn-OPDA may not be the only bioactive jasmonate and COI1 ligand in Marchantia.

中文翻译：

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十六碳三烯酸的合成需要一种进化上古老的脂肪酸去饱和酶，十六碳三烯酸是多形金缕梅生物活性茉莉酸盐的主要来源

• 茉莉酸是脂肪酸衍生的激素，可调节植物发育、生长和应激反应的多个方面。生物活性茉莉酸酯，定义为保守 COI1 受体的配体，在维管植物和苔藓植物（茉莉酰-l-异亮氨酸 (JA-Ile) 和 dinor-12-oxo-10,15( Z )-植物二烯酸 (dn-OPDA) ）， 分别）。已经阐明了模型维管植物拟南芥中JA-Ile的生物合成途径。然而，苔藓植物中 dn-OPDA 生物合成的细节仍不清楚。
• 在这里，我们在模型地钱Marchantia polymorpha中鉴定出拟南芥脂肪酸去饱和酶5 (AtFAD5)的直系同源物，并表明FAD5 功能在相隔超过4.5 亿年(Myr) 的独立进化的物种之间是古老且保守的。与 AtFAD5 类似，MpFAD5 是合成 7 Z-十六碳烯酸所必需的。因此，在 Mp fad5突变体中，十六烷类途径被阻断，dn-OPDA 浓度几乎完全耗尽，正常的叶绿体发育受损。
• 我们的研究结果表明，Marchantia中创伤诱导的 dn-OPDA 的主要来源是十六烷类途径，而十八烷类途径（即来自 OPDA）的贡献最小。
• 值得注意的是，尽管 dn-OPDA 浓度极低，但 MpCOI1 介导的对伤害和昆虫进食的反应仍然可以在 Mp fad5中激活，这表明 dn-OPDA 可能不是Marchantia中唯一的生物活性茉莉酸和 COI1 配体。