Gupta Alok K, Schauvinhold Ines, Pichersky Eran, Schiestl Florian P
Institute of Systematic Botany, University of Zurich, 8008, Zurich, Switzerland,
Funct Integr Genomics. 2014 Dec;14(4):779-88. doi: 10.1007/s10142-014-0397-9. Epub 2014 Sep 20.
Floral signaling, especially through floral scent, is often highly complex, and little is known about the molecular mechanisms and evolutionary causes of this complexity. In this study, we focused on the evolution of "floral scent genes" and the associated changes in their functions in three closely related orchid species of the genus Gymnadenia. We developed a benchmark repertoire of 2,571 expressed sequence tags (ESTs) in Gymnadenia odoratissima. For the functional characterization and evolutionary analysis, we focused on eugenol synthase, as eugenol is a widespread and important scent compound. We obtained complete coding complementary DNAs (cDNAs) of two copies of putative eugenol synthase genes in each of the three species. The proteins encoded by these cDNAs were characterized by expression and testing for activity in Escherichia coli. While G. odoratissima and Gymnadenia conopsea enzymes were found to catalyze the formation of eugenol only, the Gymnadenia densiflora proteins synthesize eugenol, as well as a smaller amount of isoeugenol. Finally, we showed that the eugenol and isoeugenol producing gene copies of G. densiflora are evolutionarily derived from the ancestral genes of the other species producing only eugenol. The evolutionary switch from production of one to two compounds evolved under relaxed purifying selection. In conclusion, our study shows the molecular bases of eugenol and isoeugenol production and suggests that an evolutionary transition in a single gene can lead to an increased complexity in floral scent emitted by plants.
花香信号传导，尤其是通过花香进行的信号传导，通常非常复杂，而对于这种复杂性的分子机制和进化原因我们知之甚少。在本研究中，我们聚焦于香兰属三种近缘兰花物种中“花香基因”的进化及其功能的相关变化。我们开发了一个包含2571个香花兰表达序列标签（EST）的基准文库。为了进行功能表征和进化分析，我们重点研究了丁香酚合酶，因为丁香酚是一种广泛存在且重要的香味化合物。我们在这三个物种中分别获得了两个推定丁香酚合酶基因拷贝的完整编码互补DNA（cDNA）。通过在大肠杆菌中的表达和活性测试对这些cDNA编码的蛋白质进行了表征。虽然发现香花兰和康氏香兰的酶仅催化丁香酚的形成，但密花兰的蛋白质能合成丁香酚以及少量异丁香酚。最后，我们表明密花兰中产生丁香酚和异丁香酚的基因拷贝在进化上源自其他仅产生丁香酚物种的祖先基因。从产生一种化合物到产生两种化合物的进化转变是在宽松的纯化选择下发生的。总之，我们的研究揭示了丁香酚和异丁香酚产生的分子基础，并表明单个基因的进化转变可导致植物释放的花香复杂性增加。
