College of Horticulture, Nanjing Agricultural University, Nanjing 210095, China.
Department of Plant Sciences, University of Tennessee, Knoxville, TN 37996, USA.
Phytochemistry. 2021 Nov;191:112899. doi: 10.1016/j.phytochem.2021.112899. Epub 2021 Sep 1.
Among the factors that have made flowering plants the most species-rich lineage of land plants is the interaction between flower and insect pollinators, for which floral scent plays a pivotal role. Water lilies belong to the ANA (Amborellales, Nymphaeales, and Austrobaileyales) grade of basal flowering plants. In this study, Victoria cruziana was investigated as a model night-blooming water lily for floral scent biosynthesis. Four volatile compounds, including three benzenoids and one fatty acid methyl ester methyl hexanoate, were detected from the flowers of V. cruziana during their first bloom, with methyl hexanoate accounting for 45 % of total floral volatile emission. Emission rates were largely constant before significant drop starting at the end of second bloom. To understand the molecular basis of floral scent biosynthesis in V. cruziana, particularly methyl hexanoate, a transcriptome from the whole flowers at the full-bloom stage was created and analyzed. Methyl hexanoate was hypothesized to be biosynthesized by SABATH methyltransferases. From the transcriptome, three full-length SABATH genes designated VcSABATH1-3 were identified. A full-length cDNA for each of the three VcSABATH genes was expressed in Escherichia coli to produce recombinant proteins. When tested in in vitro methyltransferase enzyme assays with different fatty acids, both VcSABATH1 and VcSABATH3 exhibited highest levels of activity with hexanoic acid to produce methyl hexanoate, with the specific activity of VcSABATH1 being about 15 % of that for VcSABATH3. VcSABATH1 and VcSABATH3 showed the highest levels of expression in stamen and pistil, respectively. In phylogenetic analysis, three VcSABATH genes clustered with other water lily SABATH methyltransferase genes including the one known for making other fatty acid methyl esters, implying both a common evolutionary origin and functional divergence. Fatty acid methyl esters are not frequent constituents of floral scents of mesangiosperms, pointing to the importance for the evolution of novel fatty acid methyltransferase for making fatty acid methyl esters in the pollination biology of water lilies.
在使开花植物成为陆地植物中物种最丰富的谱系的因素中,花与昆虫传粉者的相互作用起着关键作用,而花的香气则起着关键作用。睡莲属于 ANA(Amborellales、Nymphaeales 和 Austrobaileyales)级别的基础开花植物。在这项研究中,维多利亚·克鲁齐亚纳(Victoria cruziana)被用作模型夜开睡莲,用于研究花香生物合成。从维多利亚·克鲁齐亚纳(Victoria cruziana)的花朵中检测到四种挥发性化合物,包括三种苯丙素和一种脂肪酸甲酯——己酸甲酯,在第一次开花时,己酸甲酯占总花香挥发物的 45%。在第二次开花结束时,挥发率在显著下降之前基本保持不变。为了了解维多利亚·克鲁齐亚纳(Victoria cruziana)花香生物合成的分子基础,特别是己酸甲酯,我们创建并分析了整个花朵在盛开阶段的转录组。假设己酸甲酯是由 SABATH 甲基转移酶生物合成的。从转录组中,鉴定出三个全长 SABATH 基因,分别命名为 VcSABATH1-3。三个 VcSABATH 基因的全长 cDNA 在大肠杆菌中表达,产生重组蛋白。在不同脂肪酸的体外甲基转移酶酶测定中,VcSABATH1 和 VcSABATH3 均与己酸表现出最高的活性,生成己酸甲酯,VcSABATH1 的比活性约为 VcSABATH3 的 15%。VcSABATH1 和 VcSABATH3 在雄蕊和雌蕊中的表达水平最高。在系统发育分析中,三个 VcSABATH 基因与其他睡莲 SABATH 甲基转移酶基因聚类,包括已知产生其他脂肪酸甲酯的基因,这表明它们具有共同的进化起源和功能分化。脂肪酸甲酯不是中被子植物花香的常见成分,这表明在睡莲的传粉生物学中,新型脂肪酸甲基转移酶对于生成脂肪酸甲酯的进化具有重要意义。