Abstract
Plant specialized metabolites modulate developmental and ecological functions and comprise many therapeutic and other high-value compounds. However, the mechanisms determining their cell-specific expression remain unknown. Here we describe the transcriptional regulatory network that underlies cell-specific biosynthesis of triterpenes in Arabidopsis thaliana root tips. Expression of thalianol and marneral biosynthesis pathway genes depends on the phytohormone jasmonate and is limited to outer tissues. We show that this is promoted by the activity of redundant bHLH-type transcription factors from two distinct clades and coactivated by homeodomain factors. Conversely, the DOF-type transcription factor DAG1 and other regulators prevent expression of the triterpene pathway genes in inner tissues. We thus show how precise expression of triterpene biosynthesis genes is determined by a robust network of transactivators, coactivators and counteracting repressors.
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Data availability
The scRNAseq data are accessible via an online browser tool (http://bioit3.irc.ugent.be/plant-sc-atlas/) and raw data are deposited at NCBI with GEO numbers GSE179820 and GSE212826 for the mock- and JA-treated root tips, respectively. All other data generated for this study are included either in the main paper, Extended Data, or the Supplementary Information. Material requests should be directed to the corresponding author. Published data for TF motif mapping were retrieved from CisBP 2.00 (downloaded in December 2019: http://cisbp.ccbr.utoronto.ca/) and JASPAR2020 (https://jaspar.genereg.net/). The regulatory regions used for motif mapping were downloaded from PLAZA Dicots 4.5 (https://bioinformatics.psb.ugent.be/plaza/versions/plaza_v4_5_dicots/). Source data are provided with this paper.
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Acknowledgements
This Article was written in loving memory of A. Van Moerkercke (1979–2021). The authors thank A. Bleys for critically reading the manuscript; D. Gasperini for kindly sharing the ProMYCs:NLS-VENUS reporter lines, and P. Vittorioso for the dag1 mutant, ProDAG1:GUS and DAG1 over-expressing lines; J. R. Wendrich and T. Eekhout for assistance in the launching and analysis of the scRNAseq experiment; and S. Desmet and G. Goeminne from the VIB Metabolomics Core – Ghent for the thalianol profiling. This work was supported by the European Community’s Seventh Framework Program (FP7/2007–2013) under grant agreement 613692-TriForC and H2020 Program under grant agreement 760331-Newcotiana to A.G.; the Special Research Fund from Ghent University to A.G. and A.R. (project BOF18/GOA/013), and M.M. (project BOF20/GOA/012); the Flemish Government (AI Research program) to Y.S.; the Research Foundation Flanders with research project grants to A.G. (G004515N and G008417N) and a postdoctoral fellowship to P.F.-C.; a Swiss National Science Foundation postdoctoral fellowship (P300PA_177831) to M.C.; and a China Scholarship Council PhD scholarship to Y.B. A.O. acknowledges funding support from the John Innes Foundation and the BBSRC Institute Strategic Program Grant ‘Molecules from Nature – Products and Pathways’ (BBS/E/J/000PR9790).
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A.G., T.H.N., A.V.M., P.F.-C. and A.R. conceptualized the project. T.H.N., L.T., M.M., T.D., M.C., K. Verstaen, G.V.I., Y.S., B.D.R., K. Vandepoele, H.-W.N., A.O., A.R. and A.G. developed the methodology. T.H.N., Y.B., A.V.M., P.F.-C., L.T., T.D., M.C., G.V.I., A.R. and A.G. conducted the investigations. T.H.N., L.T., A.R., K. Verstaen and T.D. performed visualization. A.G, Y.S. and A.O. acquired funding. A.G. and A.R. administered the project. A.G., A.R., B.D.R., K. Vandepoele and Y.S. supervised the project. A.V.M., A.R. and A.G. wrote the original draft. T.H.N. and B.D.R. reviewed and edited the manuscript.
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Extended data
Extended Data Fig. 1
Violin plots showing cell-specific expression of the thalianol biosynthesis genes under mock and JA treatments.
Extended Data Fig. 2
Violin plots showing cell-specific expression of the marneral biosynthesis genes under mock and JA treatments.
Extended Data Fig. 3 MYC2 expression is induced by protoplasting in root tips.
a, Violin plots showing cell-specific expression of MYC2, MYC3 and MYC4 upon mock and JA treatments. b, RT-qPCR expression analysis of intact roots tips and root tip protoplasts upon mock and JA treatments. Values on the Y-axis represent fold-induction compared to mock-treated intact roots (set to 1). The error bars designate the SE of the mean (n = 3 biologically independent samples). Statistical significance was determined using the Student’s t-test (*P < 0.05, **P < 0.005, ***P < 0.0005).
Extended Data Fig. 4 Heatmap of THAS single-cell co-expression analysis.
Top 100 genes co-expressed with THAS under JA treatment across all root tip tissue types. Expression values as log fold change of JA compared to mock conditions are shown for each of the separate tissue types.
Extended Data Fig. 5 The expression of bHLH clade IVa genes is induced by JA in a COI1-dependent manner.
a, Violin plots showing cell-specific expression of bHLH18 and bHLH25 upon mock and JA treatments. b, Expression profile of ProbHLH19:GFP-GUS in wt root tips grown on mock or 50 µM JA for 24 h. Scale bars = 20 µm. At least 3 seedling roots were observed with similar results. c, RT-qPCR expression analysis of bHLH clade IV genes upon mock and JA treatments in the Col-0 wt and coi1-1 backgrounds. The error bars designate the SE of the mean (n = 3 biologically independent samples). Values on the Y-axis represent fold-induction compared to mock-treated wt (set to 1). Statistical significance was determined using the Student’s t-test (*P < 0.05, **P < 0.005, ***P < 0.0005).
Extended Data Fig. 6 Expression of bHLH clade IVa transcription factors is induced by MYCs.
a, RT-qPCR expression analysis of bHLH clade IV genes upon mock and JA treatments in the Col-0 wt and mycT backgrounds. The error bars designate the SE of the mean (n = 3 biologically independent samples). Values on the Y-axis represent fold-induction compared to mock-treated wt (set to 1). Statistical significance was determined using the Student’s t-test (*P < 0.05, **P < 0.005, ***P < 0.0005). b, Transactivation in N. tabacum protoplasts of the ProbHLH19 and ProbHLH20 fused to the fLUC reporter and cotransfected with either GUS, MYC2, MYC2D105N, bHLH19 or bHLH25. Values on the Y-axis are normalized fold-changes relative to protoplasts cotransfected with the reporter constructs and a pCaMV35S:GUS (GUS) control plasmid (set to 1). The error bars designate the SE of the mean (n = 8 biologically independent samples). Statistical significance was determined using the Student’s t-test (*P < 0.05, **P < 0.005, ***P < 0.0005).
Extended Data Fig. 7 Violin plots showing cell-specific expression of candidate root triterpene transcriptional regulators under mock- and JA-treated conditions.
Only genes from the HDG- and DOF-type families that show expression in our scRNAseq dataset are represented.
Extended Data Fig. 8 Homeodomain glabrous proteins coactivate the transcription of the THAS promoter.
Transactivation in N. tabacum protoplasts transfected with ProTHAS fused to the fLUC reporter, and cotransfected with combinations of GL2, HDG2, HDG5, MYC2D105N, bHLH19 or/and bHLH20. Values on the Y-axis are normalized fold-changes relative to protoplasts cotransfected with the reporter constructs and a pCaMV35S:GUS (GUS) control plasmid (set to 1). The error bars designate the SE of the mean (n = 8 biologically independent samples). Statistical significance was determined using the Student’s t-test (*P < 0.05, **P < 0.005, ***P < 0.0005).
Extended Data Fig. 9 vDOF1 proteins do not modulate transcription of the THAS promoter.
Transactivation in transfected N. tabacum protoplasts of the ProTHAS fused to the fLUC reporter, and cotransfected with combinations of vDOF1, MYC2D105N, bHLH19 or/and bHLH20. Values on the Y-axis are normalized fold-changes relative to protoplasts co-transfected with the reporter constructs and a pCaMV35S:GUS (GUS) control plasmid (set to 1). The error bars designate the SE of the mean (n = 8 biologically independent samples). Statistical significance was determined using the Student’s t-test (NS, Non-significant; ***P < 0.0005).
Extended Data Fig. 10
Model for the regulatory network that drives spatiotemporal expression of thalianol and marneral biosynthesis genes in Arabidopsis root tips.
Supplementary information
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Supplementary Figs. 1–8 and Tables 1–5.
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Nguyen, T.H., Thiers, L., Van Moerkercke, A. et al. A redundant transcription factor network steers spatiotemporal Arabidopsis triterpene synthesis. Nat. Plants 9, 926–937 (2023). https://doi.org/10.1038/s41477-023-01419-8
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DOI: https://doi.org/10.1038/s41477-023-01419-8