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The role of MYB34, MYB51 and MYB122 in the regulation of camalexin biosynthesis in Arabidopsis thaliana.

Frerigmann H, Glawischnig E, Gigolashvili T - Front Plant Sci (2015)

Bottom Line: The abundance of camalexin was strongly reduced in myb34/51 and myb51/122 double and in triple myb mutant, suggesting that these transcription factors are important in camalexin biosynthesis.Furthermore, expression of MYB51 and MYB122 was significantly increased by biotic and abiotic camalexin-inducing agents.In conclusion, this study reveals the importance of MYB factors regulating the generation of IAOx as precursor of camalexin.

View Article: PubMed Central - PubMed

Affiliation: Botanical Institute and Cluster of Excellence on Plant Sciences, University of Cologne, Cologne Germany.

ABSTRACT
The phytoalexin camalexin and indolic glucosinolates share not only a common evolutionary origin and a tightly interconnected biosynthetic pathway, but regulatory proteins controlling the shared enzymatic steps are also modulated by the same R2R3-MYB transcription factors. The indolic phytoalexin camalexin is a crucial defense metabolite in the model plant Arabidopsis. Indolic phytoalexins and glucosinolates appear to have a common evolutionary origin and are interconnected on the biosynthetic level: a key intermediate in the biosynthesis of camalexin, indole-3-acetaldoxime (IAOx), is also required for the biosynthesis of indolic glucosinolates and is under tight control by the transcription factors MYB34, MYB51, and MYB122. The abundance of camalexin was strongly reduced in myb34/51 and myb51/122 double and in triple myb mutant, suggesting that these transcription factors are important in camalexin biosynthesis. Furthermore, expression of MYB51 and MYB122 was significantly increased by biotic and abiotic camalexin-inducing agents. Feeding of the triple myb34/51/122 mutant with IAOx or indole-3-acetonitrile largely restored camalexin biosynthesis. Conversely, tryptophan could not complement the low camalexin phenotype of this mutant, which supports a role for the three MYB factors in camalexin biosynthesis upstream of IAOx. Consistently expression of the camalexin biosynthesis genes CYP71B15/PAD3 and CYP71A13 was not negatively affected in the triple myb mutant and the MYBs could not activate pCYP71B15::uidA expression in trans-activation assays with cultured Arabidopsis cells. In conclusion, this study reveals the importance of MYB factors regulating the generation of IAOx as precursor of camalexin.

No MeSH data available.


Induction of MYB51 and MYB122 in rosette leaves of Alc::PaNieDc plants. Expression of MYB34(A), MYB51(B), MYB122(C), CYP71A13(D), and the camalexin biosynthesis gene CYP71B15(E) following AgNO3 treatment. Relative expression in pAlc::PaNieDc was measured in leaves of 6-week-old plants induced with ethanol (for 60 min, 150 min or 300 min; time point 0 = 1 min). Data are means ± SE from two independent experiments each with three biological replicates (n = 6). Values marked with asterisks are significantly different from those of control plants (Student’s t-test; p < 0.05).
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Figure 3: Induction of MYB51 and MYB122 in rosette leaves of Alc::PaNieDc plants. Expression of MYB34(A), MYB51(B), MYB122(C), CYP71A13(D), and the camalexin biosynthesis gene CYP71B15(E) following AgNO3 treatment. Relative expression in pAlc::PaNieDc was measured in leaves of 6-week-old plants induced with ethanol (for 60 min, 150 min or 300 min; time point 0 = 1 min). Data are means ± SE from two independent experiments each with three biological replicates (n = 6). Values marked with asterisks are significantly different from those of control plants (Student’s t-test; p < 0.05).

Mentions: In addition, we analyzed transgenic plants that expressed a gene encoding a Nep1-like protein from Pythium aphanidermatum (PaNie), which acts as a PAMP, under the control of an ethanol-inducible promoter (Rauhut et al., 2009). The production of this Nep1-like protein triggers the strong accumulation of camalexin 8 h following ethanol inductions (Rauhut et al., 2009). The transcription of MYB51 significantly increased 150 min after treatment, and that of CYP71B15, CYP71A13, and MYB122 after 300 min (5 h; Figure 3). Conversely, MYB34 was not induced by PaNie expression, which confirms its minor role in camalexin regulation. A similar induction pattern of the MYBs and camalexin genes was observed upon colonization with the fungus Piriformospora indica (Lahrmann et al., 2015). In addition, MYB51 transcription was also increased 40 and 88 h after infection with the necrotrophic pathogen B. cinerea, as revealed by the pMYB51::GUS reporter (Supplementary Figure S1).


The role of MYB34, MYB51 and MYB122 in the regulation of camalexin biosynthesis in Arabidopsis thaliana.

Frerigmann H, Glawischnig E, Gigolashvili T - Front Plant Sci (2015)

Induction of MYB51 and MYB122 in rosette leaves of Alc::PaNieDc plants. Expression of MYB34(A), MYB51(B), MYB122(C), CYP71A13(D), and the camalexin biosynthesis gene CYP71B15(E) following AgNO3 treatment. Relative expression in pAlc::PaNieDc was measured in leaves of 6-week-old plants induced with ethanol (for 60 min, 150 min or 300 min; time point 0 = 1 min). Data are means ± SE from two independent experiments each with three biological replicates (n = 6). Values marked with asterisks are significantly different from those of control plants (Student’s t-test; p < 0.05).
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Related In: Results  -  Collection

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Show All Figures
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Figure 3: Induction of MYB51 and MYB122 in rosette leaves of Alc::PaNieDc plants. Expression of MYB34(A), MYB51(B), MYB122(C), CYP71A13(D), and the camalexin biosynthesis gene CYP71B15(E) following AgNO3 treatment. Relative expression in pAlc::PaNieDc was measured in leaves of 6-week-old plants induced with ethanol (for 60 min, 150 min or 300 min; time point 0 = 1 min). Data are means ± SE from two independent experiments each with three biological replicates (n = 6). Values marked with asterisks are significantly different from those of control plants (Student’s t-test; p < 0.05).
Mentions: In addition, we analyzed transgenic plants that expressed a gene encoding a Nep1-like protein from Pythium aphanidermatum (PaNie), which acts as a PAMP, under the control of an ethanol-inducible promoter (Rauhut et al., 2009). The production of this Nep1-like protein triggers the strong accumulation of camalexin 8 h following ethanol inductions (Rauhut et al., 2009). The transcription of MYB51 significantly increased 150 min after treatment, and that of CYP71B15, CYP71A13, and MYB122 after 300 min (5 h; Figure 3). Conversely, MYB34 was not induced by PaNie expression, which confirms its minor role in camalexin regulation. A similar induction pattern of the MYBs and camalexin genes was observed upon colonization with the fungus Piriformospora indica (Lahrmann et al., 2015). In addition, MYB51 transcription was also increased 40 and 88 h after infection with the necrotrophic pathogen B. cinerea, as revealed by the pMYB51::GUS reporter (Supplementary Figure S1).

Bottom Line: The abundance of camalexin was strongly reduced in myb34/51 and myb51/122 double and in triple myb mutant, suggesting that these transcription factors are important in camalexin biosynthesis.Furthermore, expression of MYB51 and MYB122 was significantly increased by biotic and abiotic camalexin-inducing agents.In conclusion, this study reveals the importance of MYB factors regulating the generation of IAOx as precursor of camalexin.

View Article: PubMed Central - PubMed

Affiliation: Botanical Institute and Cluster of Excellence on Plant Sciences, University of Cologne, Cologne Germany.

ABSTRACT
The phytoalexin camalexin and indolic glucosinolates share not only a common evolutionary origin and a tightly interconnected biosynthetic pathway, but regulatory proteins controlling the shared enzymatic steps are also modulated by the same R2R3-MYB transcription factors. The indolic phytoalexin camalexin is a crucial defense metabolite in the model plant Arabidopsis. Indolic phytoalexins and glucosinolates appear to have a common evolutionary origin and are interconnected on the biosynthetic level: a key intermediate in the biosynthesis of camalexin, indole-3-acetaldoxime (IAOx), is also required for the biosynthesis of indolic glucosinolates and is under tight control by the transcription factors MYB34, MYB51, and MYB122. The abundance of camalexin was strongly reduced in myb34/51 and myb51/122 double and in triple myb mutant, suggesting that these transcription factors are important in camalexin biosynthesis. Furthermore, expression of MYB51 and MYB122 was significantly increased by biotic and abiotic camalexin-inducing agents. Feeding of the triple myb34/51/122 mutant with IAOx or indole-3-acetonitrile largely restored camalexin biosynthesis. Conversely, tryptophan could not complement the low camalexin phenotype of this mutant, which supports a role for the three MYB factors in camalexin biosynthesis upstream of IAOx. Consistently expression of the camalexin biosynthesis genes CYP71B15/PAD3 and CYP71A13 was not negatively affected in the triple myb mutant and the MYBs could not activate pCYP71B15::uidA expression in trans-activation assays with cultured Arabidopsis cells. In conclusion, this study reveals the importance of MYB factors regulating the generation of IAOx as precursor of camalexin.

No MeSH data available.