Biosynthesis of Phenolic Glycosides from Phenylpropanoid and Benzenoid Precursors in Populus

School of Forest Resources and Environmental Science, Michigan Technological University, Houghton, MI 49931, USA.
Journal of Chemical Ecology (Impact Factor: 2.75). 02/2010; 36(3):286-97. DOI: 10.1007/s10886-010-9757-7
Source: PubMed


Salicylate-containing phenolic glycosides (PGs) are abundant and often play a dominant role in plant-herbivore interactions of Populus and Salix species (family Salicaceae), but the biosynthetic pathway to PGs remains unclear. Cinnamic acid (CA) is thought to be a precursor of the salicyl moiety of PGs. However, the origin of the 6-hydroxy-2-cyclohexen-on-oyl (HCH) moiety found in certain PGs, such as salicortin, is not known. HCH is of interest because it confers toxicity and antifeedant properties against herbivores. We incubated Populus nigra leaf tissue with stable isotope-labeled CA, benzoates, and salicylates, and measured isotopic incorporation levels into both salicin, the simplest PG, and salicortin. Labeling of salicortin from [13C6]-CA provided the first evidence that HCH, like the salicyl moiety, is a phenylpropanoid derivative. Benzoic acid and benzaldehyde also labeled both salicyl and HCH, while benzyl alcohol labeled only the salicyl moiety in salicortin. Co-administration of unlabeled benzoates with [13C6]-CA confirmed their contribution to the biosynthesis of the salicyl but not the HCH moiety of salicortin. These data suggest that benzoate interconversions may modulate partitioning of phenylpropanoids to salicyl and HCH moieties, and hence toxicity of PGs. Surprisingly, labeled salicyl alcohol and salicylaldehyde were readily converted to salicin, but did not result in labeled salicortin. Co-administration of unlabeled salicylates with labeled CA suggested that salicyl alcohol and salicylaldehyde may have inhibited salicortin biosynthesis. A revised metabolic grid model of PG biosynthesis in Populus is proposed, providing a guide for functional genomic analysis of the PG biosynthetic pathway.

Download full-text


Available from: Chung-Jui Tsai,
80 Reads
  • Source
    • "This reaction could theoretically be a source of salicyl benzoate (33), which might then be converted to salicyl HCH (36) (salicyl hydroxy-2-cyclohexen-one) and salicortin (2) directly. However, this scheme contradicts the model proposed by Babst et al. (2010), and the authors' experimental data showed a lack of conversion of salicyl alcohol (8) to salicortin (2), though the label does readily become incorporated into salicin (1). This would suggest that there is no direct conversion from salicyl alcohol (8) to salicortin (2), as might be proposed if PtSABT is within the core pathway. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Salicinoids are phenolic glycosides (PGs) characteristic of the Salicaceae and are known defenses against insect herbivory. Common examples are salicin, salicortin, tremuloidin, and tremulacin, which accumulate to high concentrations in the leaves and bark of willows and poplars. Although their biosynthetic pathway is not known, recent work has suggested that benzyl benzoate may be a potential biosynthetic intermediate. Two candidate genes, named PtACT47 and PtACT49, encoding BAHD-type acyl transferases were identified and are predicted to produce such benzylated secondary metabolites. Herein described are the cDNA cloning, heterologous expression and in vitro functional characterization of these two BAHD acyltransferases. Recombinant PtACT47 exhibited low substrate selectivity and could utilize acetyl-CoA, benzoyl-CoA, and cinnamoyl-CoA as acyl donors with a variety of alcohols as acyl acceptors. This enzyme showed the greatest Km/Kcat ratio (45.8 nM-1 s-1) and lowest Km values (45.1 uM) with benzoyl-CoA and salicyl alcohol, and was named benzoyl-CoA: salicyl alcohol O-benzoyltransferase (PtSABT). Recombinant PtACT49 utilized a narrower range of substrates, including benzoyl-CoA and acetyl-CoA and a limited number of alcohols. Its highest Km/Kcat (31.8 nM-1 s-1) and lowest Km (55.3 uM) were observed for benzoyl-CoA and benzyl alcohol, and it was named benzoyl-CoA: benzyl alcohol O-benzoyltransferase (PtBEBT). Both enzymes were also capable of synthesizing plant volatile alcohol esters, such as hexenyl benzoate, at trace levels. Although the activities demonstrated are consistent with roles in salicinoid biosynthesis, direct tests of this hypothesis using transgenic poplar must still be performed.
    Phytochemistry 05/2015; 113:149-159. DOI:10.1016/j.phytochem.2014.10.018 · 2.55 Impact Factor
  • Source
    • "Radiolabelled salicylaldehyde 23 was readily glucosyled to yield b-D-helacin 30 when fed to S. purpurea which, subsequently underwent reduction at the carbonyl group to give b-D-salicin 1 [7] [16]. In addition, using radiolabelled b-D-helacin 30 undergoes similar reduction to give b-D-salicin 1 [27]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Beta-D-Salicin 1 (Mahdi et al. [8]) is an interesting medicinal phytochemical that exhibits cross functions in plants and humans immunologically. This molecule 1 (Mahdi et al. [8]) has attracted the attention of scientists in various interdisciplinary fields, including chemistry, pharmacology and medicine. The biological cross functions of b-D-salicin 1 (Mahdi et al. [8]) serve in plant survival and healing processes via salicylic acid 2 (Pierpont [23]). Thus, this raise a question whether plant biosynthesis and human metabolism crosstalk to induce therapy via molecular recognition. If so, biotechnology and bioinformatics are significant techniques for new strategies in drug development. Thus, understanding the biosynthesis, metabolism and the cross-molecular setting of recognition may encourage further discussion and research on its medicinal and biological activity virtues. ã 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (
    Biotechnology Reports 12/2014; 4(1). DOI:10.1016/j.btre.2014.08.005
  • Source
    • "However, the utilization of SA as a direct precursor for PG biosynthesis has not been supported by feeding or tracer experiments (Zenk, 1967; Payyavula et al., 2009; Babst et al., 2010) or by transgenic expression of bacterial SA hydroxylase (NahG) in Populus (Morse et al., 2007). Regardless, both SA and PGs share the same phenylpropanoid origin in Populus (Yuan et al., 2009; Babst et al., 2010), suggesting a potential metabolic link that may be sensitive to various defense and adaptive functions. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Salicylic acid (SA) has long been implicated in plant responses to oxidative stress. SA overproduction in Arabidopsis thaliana leads to dwarfism, making in planta assessment of SA effects difficult in this model system. We report that transgenic Populus tremula × alba expressing a bacterial SA synthase hyperaccumulated SA and SA conjugates without negative growth consequences. In the absence of stress, endogenously elevated SA elicited widespread metabolic and transcriptional changes that resembled those of wild-type plants exposed to oxidative stress-promoting heat treatments. Potential signaling and oxidative stress markers azelaic and gluconic acids as well as antioxidant chlorogenic acids were strongly coregulated with SA, while soluble sugars and other phenylpropanoids were inversely correlated. Photosynthetic responses to heat were attenuated in SA-overproducing plants. Network analysis identified potential drivers of SA-mediated transcriptome rewiring, including receptor-like kinases and WRKY transcription factors. Orthologs of Arabidopsis SA signaling components NON-EXPRESSOR OF PATHOGENESIS-RELATED GENES1 and thioredoxins were not represented. However, all members of the expanded Populus nucleoredoxin-1 family exhibited increased expression and increased network connectivity in SA-overproducing Populus, suggesting a previously undescribed role in SA-mediated redox regulation. The SA response in Populus involved a reprogramming of carbon uptake and partitioning during stress that is compatible with constitutive chemical defense and sustained growth, contrasting with the SA response in Arabidopsis, which is transient and compromises growth if sustained.
    The Plant Cell 07/2013; 25:2714-2730. DOI:10.1105/tpc.113.112839 · 9.34 Impact Factor
Show more