Divergent evolution of oxidosqualene cyclases in plants

Abstract

Summary• Triterpenes are one of the largest classes of plant metabolites and have important functions. A diverse array of triterpenoid skeletons are synthesized via the isoprenoid pathway by enzymatic cyclization of 2,3-oxidosqualene. The genomes of the lower plants Chlamydomonas reinhardtii and moss (Physcomitrella patens) contain just one oxidosqualene cyclase (OSC) gene (for sterol biosynthesis), whereas the genomes of higher plants contain nine to 16 OSC genes.• Here we carry out functional analysis of rice OSCs and rigorous phylogenetic analysis of 96 OSCs from higher plants, including Arabidopsis thaliana, Oryza sativa, Sorghum bicolor and Brachypodium distachyon.• The functional analysis identified an amino acid sequence for isoarborinol synthase (OsIAS) (encoded by Os11g35710 ⁄ OsOSC11) in rice. Our phylogenetic analysis suggests that expansion of OSC members in higher plants has occurred mainly through tandem duplication followed by positive selection and diversifying evolution, and consolidated the previous suggestion that dicot triterpene synthases have been derived from an ancestral lanosterol synthase instead of directly from their cycloartenol synthases.• The phylogenetic trees are consistent with the reaction mechanisms of the protosteryl and dammarenyl cations which parent a wide variety of triterpene skeletal types, allowing us to predict the functions of the uncharacterized OSCs.

Synthesis of arborane triterpenols by a bacterial oxidosqualene cyclase

“…Phylogenetic analysis of an isoarborinol synthase (IAS) from Oryza sativa (rice) demonstrated that it was recently derived from a plant cycloartenol synthase (6). Our analysis demonstrates that E. adriatica EUS is phylogenetically distinct from O. sativa IAS and most likely was not acquired via horizontal gene transfer from a plant source.…”

“…has the pentacyclic structure similar to a bacterial hopanoid (23). Various hopanoid, sterol, and plant triterpenoid synthases have been characterized, including a rice isoarborinol synthase (IAS) (6). However, a microbial enzyme that cyclizes oxidosqualene in the CBC conformation to an arborinol lipid has yet to be identified.…”

“…An arborinol synthase represents a unique combination of these characteristics. It is similar to a sterol cyclase in that it cyclizes oxidosqualene in the CBC conformation (6,7,23) but differs in that its final product Significance Polycyclic lipids produced by bacteria and eukaryotes can be preserved in sedimentary rocks for millions of years. These ancient lipids can function as "molecular fossils" or biomarkers that can inform us about the types of organisms and environments on early Earth.…”

Glycosyltransferases from Oat (Avena) Implicated in the Acylation of Avenacins

“…This will open up opportunities to carry out functional analysis in planta using reverse genetics, with the aim of identifying mutations in UGT74H5, UGT74H6, and other target genes of interest and assessing the role of these genes in specialized metabolism, plant defense, and other important crop traits. UGT74H5 and UGT74H6 now form part of the growing tool kit of characterized genes and enzymes available from plants that can be deployed for triterpene metabolic engineering for disease control and synthetic biology applications (41)(42)(43).…”

Molecular characterization and differential expression studies of an oxidosqualene cyclase (OSC) gene of Brahmi (Bacopa monniera)

“…For example, β-amyrin synthase and cycloartenol synthase from P. ginseng (Kushiro et al 1998), five OSCs from Kalanchoe daigremontiana (Wang et al 2010), dammaranediol synthase from Centella asiatica (Kim et al 2009), β-amyrin synthase from Aster sedifolius and Arabidopsis thaliana (Shibuya et al 2009) and OSC from Aster tataricus and tomato (Wang et al 2011;Sawai et al 2011), have been cloned and functionally characterized in mutant yeast strain GIL77, having lanosterol synthase deficiency. The catalytic functions of several plants OSCs have been studied using the S. cerevisiae yeast mutants and Pichia pastoris strains (Kajikawa et al 2005;Ito et al 2011;Xue et al 2012;Sun et al 2013). Confalonieri et al (2009) over-expressed the Aster sodifolius β-amyrin synthase (AsOXA1) in Medicago truncatula and observed significantly higher amount of some triterpenes accumulation in leaf and roots.…”