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BackgroundLabdane-related diterpenoids form the largest group among the diterpenes. They fulfill important functions in primary metabolism as essential plant growth hormones and are known to function in secondary metabolism as, for example, phytoalexins. The biosynthesis of labdane-related diterpenes is mediated by the action of class II and class I diterpene synthases. Although terpene synthases have been well investigated in poplar, little is known about diterpene formation in this woody perennial plant species.ResultsThe recently sequenced genome of Populus trichocarpa possesses two putative copalyl diphosphate synthase genes (CPS, class II) and two putative kaurene synthase genes (KS, class I), which most likely arose through a genome duplication and a recent tandem gene duplication, respectively. We showed that the CPS-like gene PtTPS17 encodes an ent-copalyl diphosphate synthase (ent-CPS), while the protein encoded by the putative CPS gene PtTPS18 showed no enzymatic activity. The putative kaurene synthases PtTPS19 and PtTPS20 both accepted ent-copalyl diphosphate (ent-CPP) as substrate. However, despite their high sequence similarity, they produced different diterpene products. While PtTPS19 formed exclusively ent-kaurene, PtTPS20 generated mainly the diterpene alcohol, 16α-hydroxy-ent-kaurane. Using homology-based structure modeling and site-directed mutagenesis, we demonstrated that one amino acid residue determines the different product specificity of PtTPS19 and PtTPS20. A reciprocal exchange of methionine 607 and threonine 607 in the active sites of PtTPS19 and PtTPS20, respectively, led to a complete interconversion of the enzyme product profiles. Gene expression analysis revealed that the diterpene synthase genes characterized showed organ-specific expression with the highest abundance of PtTPS17 and PtTPS20 transcripts in poplar roots.ConclusionsThe poplar diterpene synthases PtTPS17, PtTPS19, and PtTPS20 contribute to the production of ent-kaurene and 16α-hydroxy-ent-kaurane in poplar. While ent-kaurene most likely serves as the universal precursor for gibberellins, the function of 16α-hydroxy-ent-kaurane in poplar is not known yet. However, the high expression levels of PtTPS20 and PtTPS17 in poplar roots may indicate an important function of 16α-hydroxy-ent-kaurane in secondary metabolism in this plant organ.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0647-6) contains supplementary material, which is available to authorized users.

Plants use secondary metabolites such as polyphenols for chemical defense against pathogens and herbivores. Despite their importance in plant pathogen interactions and tolerance to diseases,i tr emains challenging to detect polyphenols in complex plant tissues.H ere,w ec reate molecular sensors for plant polyphenol imaging that are based on nearinfrared (NIR) fluorescent single-wall carbon nanotubes (SWCNTs). We identified polyethylene glycol-phospholipids that render (6,5)-SWCNTs sensitive (K d = 90 nM) to plant polyphenols (tannins,f lavonoids,… ), whichr ed-shift (up to 20 nm) and quenchtheir emission (ca. 1000 nm). These sensors report changes in total polyphenol level after herbivore or pathogen challenge in crop plant systems (Soybean Glycine max) and leaf tissue extracts (Tococa spp.). We furthermore demonstrate remote chemical imaging of pathogen-induced polyphenol release from roots of soybean seedlings over the time course of 24 h. This approach allows in situ visualization and understanding of the chemical plant defense in real time and paves the way for plant phenotyping for optimized polyphenol secretion.

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