Double-barreled defense: dual ent-miltiradiene synthases in most rice cultivars

Rice(Oryza sativa)produces numerous diterpenoid phytoalexins that are important in defense against pathogens.Surprisingly,despite extensive previous investigations,a major group of such phytoalexins,the abietoryzins,were only recently reported.These aromatic abietanes are presumably derived from ent-miltiradiene,but such biosynthetic capacity has not yet been reported in O.sativa.While wild rice has been reported to contain such an enzyme,specifically ent-kaurene synthase-like 10(KSL10),the only characterized ortholog from O.sativa(OsKSL10),specifically from the well-studied cultivar(cv.)Nipponbare,instead has been shown to make ent-sandaracopimaradiene,precursor to the oryzalexins.Notably,in many other cultivars,OsKSL10 is accompanied by a tandem duplicate,termed here OsKSL14.Biochemical characterization of OsKLS14 from cv.Kitaake demonstrates that this produces the expected abietoryzin precursor ent-miltiradiene.Strikingly,phylogenetic analysis of OsKSL10 across the rice pan-genome reveals that from cv.Nipponbare is an outlier,whereas the alleles from most other cultivars group with those from wild rice,suggesting that these also might produce ent-miltiradiene.Indeed,OsKSL10 from cv.Kitaake exhibits such activity as well,consistent with its production of abietoryzins but not oryzalexins.Similarly consistent with these results is the lack of abietoryzin production by cv.Nipponbare.Although their equivalent product outcome might suggest redundancy,OsKSL10 and OsKSL14 were observed to exhibit distinct expression patterns,indicating such differences may underlie retention of these duplicated genes.Regardless,the results reported here clarify abietoryzin biosynthesis and provide insight into the evolution of rice diterpenoid phytoalexins.

Functional identification of the terpene synthase family involved in diterpenoid alkaloids biosynthesis in Aconitum carmichaelii

Aconitum carmichaelii is a high-value medicinal herb widely used across China,Japan,and other Asian countries.Aconitine-type diterpene alkaloids(DAs)are the characteristic compounds in Aconitum.Although six transcriptomes,based on short-read next generation sequencing technology,have been reported from the Aconitum species,the terpene synthase(TPS)corresponding to DAs biosynthesis remains unidentified.We apply a combination of Pacbio isoform sequencing and RNA sequencing to provide a comprehensive view of the A.carmichaelii transcriptome.Nineteen TPSs and five alternative splicing isoforms belonging to TPS-b,TPS-c,and TPS-e/f subfamilies were identified.In vitro enzyme reaction analysis functional identified two sesqui-TPSs and twelve di TPSs.Seven of the TPS-c subfamily genes reacted with GGPP to produce the intermediate ent-copalyl diphosphate.Five Ac KSLs separately reacted with ent-CPP to produce ent-kaurene,ent-atiserene,and ent-13-epi-sandaracopimaradie:a new diterpene found in Aconitum.Ac TPSs gene expression in conjunction DAs content analysis in different tissues validated that ent-CPP is the sole precursor to all DAs biosynthesis,with Ac KSL1,Ac KSL2 s and Ac KSL3-1 responsible for C20 atisine and napelline type DAs biosynthesis,respectively.These data clarified the molecular basis for the C20-DAs biosynthetic pathway in A.carmichaelii and pave the way for further exploration of C19-DAs biosynthesis in the Aconitum species.

Mechanistic analysis for the origin of diverse diterpenes in Tripterygium wilfordii

Tripterygium wilfordii is a valuable medicinal plant rich in biologically active diterpenoids,but there are few studies on the origins of these diterpenoids in its secondary metabolism.Here,we identified three regions containing tandemly duplicated diterpene synthase genes on chromosomes(Chr) 17 and 21 of T. wilfordii and obtained 11 diterpene synthases with different functions.We farther revealed that these diterpene synthases underwent duplication and rearrangement at approximately 2.3-23.7 million years ago(MYA) by whole-genome triplication(WGT),transposon mediation,and tandem duplication,followed by functional divergence.We first demonstrated that four key amino acids in the sequences of TwCPS3,TwCPS5,and TwCPSS were altered during evolution,leading to their functional divergence and the formation of diterpene secondary metabolites.Then,we demonstrated that the functional divergence of three TwKSLs was driven by mutations in two key amino acids.Finally,we discovered the mechanisms of evolution and pseudogenization of miltiradiene synthases in T.wilfordii and elucidated that the new function in TwMS1/2 from the terpene synthase(TPS)-b subfamily was caused by progressive changes in multiple amino acids after the WGT event.Our results provide key evidence for the formation of diverse diterpenoids during the evolution of secondary metabolites in T.wilfordii.

A review:biosynthesis of plant-derived labdane-related diterpenoids

Plant-derived labdane-related diterpenoids(LRDs)represent a large group of terpenoids.LRDs possess either a labdane-type bicyclic core structure or more complex ring systems derived from labdane-type skeletons,such as abietane,pimarane,kaurane,etc.Due to their various pharmaceutical activities and unique properties,many of LRDs have been widely used in pharmaceutical,food and perfume industries.Biosynthesis of various LRDs has been extensively studied,leading to characterization of a large number of new biosynthetic enzymes.The biosynthetic pathways of important LRDs and the relevant enzymes(especially diterpene synthases and cytochrome P450 enzymes)were summarized in this review.