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. 2008 Dec 22:8:132.
doi: 10.1186/1471-2229-8-132.

Elicitor-induced transcription factors for metabolic reprogramming of secondary metabolism in Medicago truncatula

Marina A Naoumkina  1 , XianZhi He, Richard A Dixon
Affiliations

Elicitor-induced transcription factors for metabolic reprogramming of secondary metabolism in Medicago truncatula

Marina A Naoumkina et al. BMC Plant Biol. .

Abstract

Background: Exposure of Medicago truncatula cell suspension cultures to pathogen or wound signals leads to accumulation of various classes of flavonoid and/or triterpene defense molecules, orchestrated via a complex signalling network in which transcription factors (TFs) are essential components.

Results: In this study, we analyzed TFs responding to yeast elicitor (YE) or methyl jasmonate (MJ). From 502 differentially expressed TFs, WRKY and AP2/EREBP gene families were over-represented among YE-induced genes whereas Basic Helix-Loop-Helix (bHLH) family members were more over-represented among the MJ-induced genes. Jasmonate ZIM-domain (JAZ) transcriptional regulators were highly induced by MJ treatment. To investigate potential involvement of WRKY TFs in signalling, we expressed four Medicago WRKY genes in tobacco. Levels of soluble and wall bound phenolic compounds and lignin were increased in all cases. WRKY W109669 also induced tobacco endo-1,3-beta-glucanase (NtPR2) and enhanced the systemic defense response to tobacco mosaic virus in transgenic tobacco plants.

Conclusion: These results confirm that Medicago WRKY TFs have broad roles in orchestrating metabolic responses to biotic stress, and that they also represent potentially valuable reagents for engineering metabolic changes that impact pathogen resistance.

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Figures

Figure 1
Figure 1
TFs regulated by YE or MJ in M. truncatula cell suspension cultures. Venn diagrams showing the numbers of transcription factors induced by YE or MJ at 2 h (A) and 24 h (B) of treatment. Up- (C) and down-regulated (D) transcription factors are classified according to [23].
Figure 2
Figure 2
Expression of WRKY transcription factors in M. truncatula cell cultures. A, induction of WRKYs by YE as revealed by oligonucleotide array analysis. The double apostrophes represent minutes and the single apostrophes represent hours. B, WRKY transcript levels in YE and MJ treated cells determined by Affymetrix array analysis. C, Detailed time course for WRKY gene transcript levels in response to YE, as determined by RT-PCR. Actin is shown as loading control.
Figure 3
Figure 3
RT-PCR analysis of Medicago W109669 and tobacco PR2 transcript levels in transgenic tobacco lines overexpressing W109669. Control plants harbored pBI121. Control and transgenic plants of the T0 generation were used for analysis. Actin is shown as loading control.
Figure 4
Figure 4
Levels of phenolic compounds in transgenic tobacco lines expressing Medicago WRKYs. Selected regions of HPLC chromatograms show soluble (A) and wall bound (B) phenolic compounds. Insets show the UV spectra of identified peaks. (C) and (D) show relative levels (peak areas) of soluble and wall bound phenolic compounds in control and transgenic lines. Control plants harbor pBI121. Error bars indicate standard error from three biological replicates (control and transgenic lines – T0 generation).
Figure 5
Figure 5
Lignin content in transgenic tobacco plants expressing Medicago WRKYs. Lignin content, determined by the acetyl bromide method, in control and transgenic tobacco plants expressing Medicago WRKY genes. Control plants harbor pBI121. Error bars indicate standard error from three biological replicates (control and transgenic lines – T0 generation).
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References

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