Mol Plant. 2018 Aug 6;11(8):1084-1096. doi: 10.1016/j.molp.2018.06.002. Epub 2018 Jun 18.
The evolution of chemical complexity has been a major driver of plant diversification, with novel compounds serving as key innovations. The species-rich mint family (Lamiaceae) produces an enormous variety of compounds that act as attractants and defense molecules in nature and are used widely by humans as flavor additives, fragrances, and anti-herbivory agents. To elucidate the mechanisms by which such diversity evolved, we combined leaf transcriptome data from 48 Lamiaceae species and four outgroups with a robust phylogeny and chemical analyses of three terpenoid classes (monoterpenes, sesquiterpenes, and iridoids) that share and compete for precursors. Our integrated chemical-genomic-phylogenetic approach revealed that: (1) gene family expansion rather than increased enzyme promiscuity of terpene synthases is correlated with mono- and sesquiterpene diversity; (2) differential expression of core genes within the iridoid biosynthetic pathway is associated with iridoid presence/absence; (3) generally, production of iridoids and canonical monoterpenes appears to be inversely correlated; and (4) iridoid biosynthesis is significantly associated with expression of geraniol synthase, which diverts metabolic flux away from canonical monoterpenes, suggesting that competition for common precursors can be a central control point in specialized metabolism. These results suggest that multiple mechanisms contributed to the evolution of chemodiversity in this economically important family.
化学复杂性的进化是植物多样化的主要驱动因素，新化合物是关键的创新。物种丰富的薄荷科（Lamiaceae）产生了大量的化合物，这些化合物在自然界中作为吸引剂和防御分子，被人类广泛用作香料添加剂、香料和抗草食性剂。为了阐明这种多样性进化的机制，我们结合了 48 种薄荷科物种和 4 个外群的叶片转录组数据，以及对三类萜烯类化合物（单萜、倍半萜和环烯醚萜）的强大系统发育和化学分析，这些化合物共享和竞争前体。我们的综合化学基因组系统发育方法揭示了：（1）萜烯合酶基因家族的扩展而不是增加酶的多功能性与单萜和倍半萜的多样性相关；（2）在环烯醚萜生物合成途径的核心基因中的差异表达与环烯醚萜的存在/缺失相关；（3）一般来说，环烯醚萜和典型单萜的产生似乎呈负相关；（4）环烯醚萜的生物合成与香叶醇合酶的表达显著相关，香叶醇合酶将代谢通量从典型的单萜中转移出来，这表明对共同前体的竞争可能是特化代谢的一个重要控制点。这些结果表明，多种机制促成了这个在经济上重要的科的化学多样性的进化。
