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Gene expression profiling and silencing reveal that monolignol biosynthesis plays a critical role in penetration defence in wheat against powdery mildew invasion.

Bhuiyan NH, Selvaraj G, Wei Y, King J - J. Exp. Bot. (2008)

Bottom Line: Co-silencing led to greater penetration of Bgt or Bgh than when the genes were silenced separately.Fluorescence emission spectra analyses revealed that gene silencing hampered host autofluorescence response at fungal contact sites.These results illustrate that monolignol biosynthesis is critically important for host defence against both appropriate and inappropriate pathogen invasion in wheat.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of Saskatchewan, Saskatoon, SK S7N 5E2, Canada. nazmul.bhuiyan@yahoo.com

ABSTRACT
Cell wall apposition (CWA) formation is one of the first lines of defence used by plants to halt invading fungi such as powdery mildew. Lignin is a complex polymer of hydroxylated and methoxylated phenylpropane units (monolignols) and lignification renders the cell wall more resistant to pathogen attack. The role of monolignol biosynthesis in CWA-mediated defence against powdery mildew penetration into cereals is demonstrated here using RNA interference (RNAi)-mediated gene silencing and enzyme-specific inhibitors. Thirteen cDNAs representing eight genes involved in monolignol biosynthesis were cloned from an expression sequence tag (EST) library derived from the epidermis of diploid wheat (Triticum monococcum) infected with Blumeria graminis f. sp. tritici (Bgt). Differential expression patterns were found for these genes in susceptible and resistant plants after infection. Transcripts of phenylalanine ammonia lyase (PAL), caffeic acid O-methyltransferase (CAOMT), ferulic acid hydroxylase (FAH), caffeoyl-CoA O-methyltransferase (CCoAMT), and cinnamyl alcohol dehydrogenase (CAD) were accumulated, particularly in the epidermis. RNAi-mediated transient gene silencing in the epidermis led to a higher penetration efficiency of Bgt than in the controls. Gene silencing also compromised penetration resistance to varying degrees with different genes against an inappropriate pathogen, B. graminis f. sp. hordei (Bgh). Co-silencing led to greater penetration of Bgt or Bgh than when the genes were silenced separately. Fluorescence emission spectra analyses revealed that gene silencing hampered host autofluorescence response at fungal contact sites. These results illustrate that monolignol biosynthesis is critically important for host defence against both appropriate and inappropriate pathogen invasion in wheat.

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The monolignol biosynthesis pathway. The grey route is the most favoured in angiosperms. All the enzymatic reactions presented in the pathway have been demonstrated at least in vitro. Because of the variety of isoenzymes and kinetic properties, alternative routes through the metabolic pathway may exist. For reactions with a question mark, the respective enzyme is unknown. PAL, phenylalanine ammonia lyase; C3H, p-coumarate 3-hydroxylase; CAOMT, caffeic acid O-methyltransferase; F5H, ferulic acid 5-hydroxylase; 4CL, 4-hydroxycinnamoyl-CoA ligase; CCoAMT, caffeoyl-CoA O-methyltransferase; CCR, cinnamoyl-CoA reductase; CAD, cinnamyl alcohol dehydrogenase; HCT, p-hydroxycinnamoyl-CoA reductase; C4H, cinnamate 4-hydoxylase.
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fig1: The monolignol biosynthesis pathway. The grey route is the most favoured in angiosperms. All the enzymatic reactions presented in the pathway have been demonstrated at least in vitro. Because of the variety of isoenzymes and kinetic properties, alternative routes through the metabolic pathway may exist. For reactions with a question mark, the respective enzyme is unknown. PAL, phenylalanine ammonia lyase; C3H, p-coumarate 3-hydroxylase; CAOMT, caffeic acid O-methyltransferase; F5H, ferulic acid 5-hydroxylase; 4CL, 4-hydroxycinnamoyl-CoA ligase; CCoAMT, caffeoyl-CoA O-methyltransferase; CCR, cinnamoyl-CoA reductase; CAD, cinnamyl alcohol dehydrogenase; HCT, p-hydroxycinnamoyl-CoA reductase; C4H, cinnamate 4-hydoxylase.

Mentions: Lignin is, after cellulose, the second most abundant terrestrial biopolymer accounting for approximately 30% of the organic carbon in the biosphere (Boerjan et al., 2003). It is crucial for the structural integrity of plant cell walls. Lignin deposition is one of the final stages of xylem cell differentiation and takes place mainly during secondary thickening of the cell wall (Chen et al., 2006). It is a complex polymer of hydroxylated and methoxylated phenylpropane units linked via oxidative coupling, probably catalysed by both peroxidases and laccases (Boudet et al., 1995). Lignin from angiosperms usually contains two major monolignols, 4-hydroxy, 3-methoxy substituted guaiacyl (G) units and 4-hydroxy, 3,5-dimethoxy substituted syringyl (S) units, joined by at least five different types of linkages (Davin and Lewis, 1992; Fig. 1).


Gene expression profiling and silencing reveal that monolignol biosynthesis plays a critical role in penetration defence in wheat against powdery mildew invasion.

Bhuiyan NH, Selvaraj G, Wei Y, King J - J. Exp. Bot. (2008)

The monolignol biosynthesis pathway. The grey route is the most favoured in angiosperms. All the enzymatic reactions presented in the pathway have been demonstrated at least in vitro. Because of the variety of isoenzymes and kinetic properties, alternative routes through the metabolic pathway may exist. For reactions with a question mark, the respective enzyme is unknown. PAL, phenylalanine ammonia lyase; C3H, p-coumarate 3-hydroxylase; CAOMT, caffeic acid O-methyltransferase; F5H, ferulic acid 5-hydroxylase; 4CL, 4-hydroxycinnamoyl-CoA ligase; CCoAMT, caffeoyl-CoA O-methyltransferase; CCR, cinnamoyl-CoA reductase; CAD, cinnamyl alcohol dehydrogenase; HCT, p-hydroxycinnamoyl-CoA reductase; C4H, cinnamate 4-hydoxylase.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2651457&req=5

fig1: The monolignol biosynthesis pathway. The grey route is the most favoured in angiosperms. All the enzymatic reactions presented in the pathway have been demonstrated at least in vitro. Because of the variety of isoenzymes and kinetic properties, alternative routes through the metabolic pathway may exist. For reactions with a question mark, the respective enzyme is unknown. PAL, phenylalanine ammonia lyase; C3H, p-coumarate 3-hydroxylase; CAOMT, caffeic acid O-methyltransferase; F5H, ferulic acid 5-hydroxylase; 4CL, 4-hydroxycinnamoyl-CoA ligase; CCoAMT, caffeoyl-CoA O-methyltransferase; CCR, cinnamoyl-CoA reductase; CAD, cinnamyl alcohol dehydrogenase; HCT, p-hydroxycinnamoyl-CoA reductase; C4H, cinnamate 4-hydoxylase.
Mentions: Lignin is, after cellulose, the second most abundant terrestrial biopolymer accounting for approximately 30% of the organic carbon in the biosphere (Boerjan et al., 2003). It is crucial for the structural integrity of plant cell walls. Lignin deposition is one of the final stages of xylem cell differentiation and takes place mainly during secondary thickening of the cell wall (Chen et al., 2006). It is a complex polymer of hydroxylated and methoxylated phenylpropane units linked via oxidative coupling, probably catalysed by both peroxidases and laccases (Boudet et al., 1995). Lignin from angiosperms usually contains two major monolignols, 4-hydroxy, 3-methoxy substituted guaiacyl (G) units and 4-hydroxy, 3,5-dimethoxy substituted syringyl (S) units, joined by at least five different types of linkages (Davin and Lewis, 1992; Fig. 1).

Bottom Line: Co-silencing led to greater penetration of Bgt or Bgh than when the genes were silenced separately.Fluorescence emission spectra analyses revealed that gene silencing hampered host autofluorescence response at fungal contact sites.These results illustrate that monolignol biosynthesis is critically important for host defence against both appropriate and inappropriate pathogen invasion in wheat.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of Saskatchewan, Saskatoon, SK S7N 5E2, Canada. nazmul.bhuiyan@yahoo.com

ABSTRACT
Cell wall apposition (CWA) formation is one of the first lines of defence used by plants to halt invading fungi such as powdery mildew. Lignin is a complex polymer of hydroxylated and methoxylated phenylpropane units (monolignols) and lignification renders the cell wall more resistant to pathogen attack. The role of monolignol biosynthesis in CWA-mediated defence against powdery mildew penetration into cereals is demonstrated here using RNA interference (RNAi)-mediated gene silencing and enzyme-specific inhibitors. Thirteen cDNAs representing eight genes involved in monolignol biosynthesis were cloned from an expression sequence tag (EST) library derived from the epidermis of diploid wheat (Triticum monococcum) infected with Blumeria graminis f. sp. tritici (Bgt). Differential expression patterns were found for these genes in susceptible and resistant plants after infection. Transcripts of phenylalanine ammonia lyase (PAL), caffeic acid O-methyltransferase (CAOMT), ferulic acid hydroxylase (FAH), caffeoyl-CoA O-methyltransferase (CCoAMT), and cinnamyl alcohol dehydrogenase (CAD) were accumulated, particularly in the epidermis. RNAi-mediated transient gene silencing in the epidermis led to a higher penetration efficiency of Bgt than in the controls. Gene silencing also compromised penetration resistance to varying degrees with different genes against an inappropriate pathogen, B. graminis f. sp. hordei (Bgh). Co-silencing led to greater penetration of Bgt or Bgh than when the genes were silenced separately. Fluorescence emission spectra analyses revealed that gene silencing hampered host autofluorescence response at fungal contact sites. These results illustrate that monolignol biosynthesis is critically important for host defence against both appropriate and inappropriate pathogen invasion in wheat.

Show MeSH
Related in: MedlinePlus