Terpene synthases (TPSs) are pivotal enzymes for the biosynthesis of terpenoids, the largest class of secondary metabolites made by plants and other organisms. To understand the basis of the vast diversification of these enzymes in plants, we investigated
Selaginella moellendorffii
, a nonseed vascular plant. The genome of this species was found to contain two distinct types of
TPS
genes. The first type of genes, which was designated as
S. moellendorffii TPS
genes (
SmTPSs
), consists of 18 members.
SmTPSs
share common ancestry with typical seed plant
TPSs
. Selected members of the
SmTPSs
were shown to encode diterpene synthases. The second type of genes, designated as
S. moellendorffii
microbial
TPS
-like genes (
SmMTPSLs
), consists of 48 members. Phylogenetic analysis showed that SmMTPSLs are more closely related to microbial TPSs than other plant TPSs. Selected SmMTPSLs were determined to function as monoterpene and sesquiterpene synthases. Most of the products formed were typical monoterpenes and sesquiterpenes that have been previously shown to be synthesized by classical plant TPS enzymes. Some in vitro products of the characterized SmMTPSLs were detected in the headspace of
S. moellendorffii
plants treated with the fungal elicitor alamethicin, showing that they are also formed in the intact plant. The presence of two distinct types of
TPSs
in the genome of
S. moellendorffii
raises the possibility that the
TPSs
in other plant species may also have more than one evolutionary origin.
萜烯合酶（TPS）是植物和其他生物合成萜烯类次生代谢产物的关键酶。为了了解植物中这些酶的广泛多样性的基础，我们研究了一种非种子植物——墨角藻。该物种的基因组发现包含两种不同类型的TPS基因。第一类基因被指定为墨角藻TPS基因（SmTPSs），由18个成员组成。SmTPSs与典型的种子植物TPS具有共同的祖先。选定的SmTPSs被证明编码二萜烯合酶。第二类基因被指定为墨角藻微生物TPS样基因（SmMTPSLs），由48个成员组成。系统发育分析表明，SmMTPSLs与微生物TPS比其他植物TPS更密切相关。选定的SmMTPSLs被确定为单萜烯和倍半萜烯合酶。大多数产物是典型的单萜烯和倍半萜烯，这些产物以前已经被证明是由经典植物TPS酶合成的。一些经过表征的SmMTPSLs的体外产物在用真菌诱导剂alamethicin处理的墨角藻植物的空气中被检测到，表明它们也在完整的植物中形成。墨角藻基因组中存在两种不同类型的TPS，这提出了其他植物物种中的TPS也可能具有不止一个进化起源的可能性。
