MTPSLs: New Terpene Synthases in Nonseed Plants.

Terpenes constitute a large class of plant secondary metabolites. It was once presumed that these compounds are biosynthesized by typical plant terpene synthases in all land plants. This view has changed with the identification of a new group of terpene synthase genes called MTPSLs for microbial terpene synthase-like genes. MTPSLs are structurally and phylogenetically more related to bacterial and fungal terpene synthases than to typical plant terpene synthases. They are widely distributed in nonseed plants but absent in seed plants and green algae. Much of the terpene diversity in nonseed plants is presumed to be determined by MTPSLs. Phylogenetic analysis suggests that ancestral MTPSL genes were acquired by early land plants from bacteria and fungi through horizontal gene transfer.