SummaryDespite the fact that Arabidopsis is largely self‐pollinating, its flowers emit a complex mixture of terpene volatiles consisting predominantly of a large group of over 20 sesquiterpenes. Here we report that only two terpene synthases, encoded by the florally expressed genes At5g23960 and At5g44630, are responsible for the formation of virtually all sesquiterpenes found in the Arabidopsis floral volatile blend. Two independent mutant lines with T‐DNA insertions in the previously identified At5g23960 gene lacked the emission of three sesquiterpenes, including the main sesquiterpene volatile (E)‐β‐caryophyllene, confirming the previous in vitro functional assignment for this gene. Flowers of a mutant line carrying a T‐DNA insertion in gene At5g44630 emitted these three sesquiterpenes, but did not emit any of the remaining sesquiterpene volatiles. An At5g44630 cDNA was expressed in Escherichia coli and the produced protein catalyzed the conversion of farnesyl diphosphate into over 15 sesquiterpenes in similar proportions to those found in the floral volatile blend. At5g23960 and At5g44630 promoter‐β‐glucuronidase (GUS) fusion experiments demonstrated that both genes are expressed in several parts of the Arabidopsis flower, with strong At5g23960 promoter‐GUS activity in the stigma and strong expression of At5g44630 in intrafloral nectaries. Given the previously reported antimicrobial activity of terpenes, their production in stigmas and nectaries may serve to inhibit microbial infection at these vulnerable sites. A survey of 37 Arabidopsis thaliana ecotypes revealed quantitative, but almost no qualitative, variations of floral monoterpene and sesquiterpene emissions suggesting that floral terpene volatiles must play some significant role in the life of the Arabidopsis plant.
摘要尽管拟南芥在很大程度上是自花授粉的,但它的花却能散发出复杂的萜烯挥发物混合物,主要由 20 多种倍半萜组成。在这里,我们报告了只有两个萜烯合成酶(由花卉表达基因 At5g23960 和 At5g44630 编码)负责拟南芥花卉挥发性混合物中几乎所有倍半萜的形成。在先前确定的 At5g23960 基因中插入 T-DNA 的两个独立突变株缺乏三种倍半萜的释放,其中包括主要的倍半萜挥发物 (E)-β-石竹烯,这证实了先前对该基因的体外功能分配。基因 At5g44630 中携带 T-DNA 插入物的突变品系的花会释放出这三种倍半萜,但不会释放出任何其余的倍半萜挥发物。At5g44630 cDNA 在大肠杆菌中表达,产生的蛋白质催化二磷酸法尼酯转化为超过 15 种倍半萜,其比例与花香挥发混合物中的比例相似。At5g23960 和 At5g44630 启动子-β-葡萄糖醛酸酶(GUS)融合实验表明,这两个基因在拟南芥花的多个部位都有表达,其中 At5g23960 启动子-GUS 在柱头有很强的活性,而 At5g44630 则在花内蜜腺有很强的表达。鉴于之前报道的萜类化合物的抗菌活性,在柱头和蜜腺中产生萜类化合物可能有助于抑制这些脆弱部位的微生物感染。对 37 个拟南芥生态型的调查显示,花单萜烯和倍半萜烯的排放量存在数量上的差异,但几乎没有质量上的差异,这表明花萜烯挥发物在拟南芥植物的生命中一定扮演着重要角色。