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

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.

9-Lipoxygenase-derived oxylipins activate brassinosteroid signaling to promote cell wall-based defense and limit pathogen infection

“…In these studies, constitutive activation of BR signaling in bes1-D and bzr1-1D mutants impaired fungal infection, suggesting cell wall reinforcement, whereas enhanced susceptibility in lox1lox5 and noxy2-2 mutants is consistent with a weakened cell wall. Cell wall lignification at the site of attempted penetration of biotrophic fungi is considered a first line of defense (Bhuiyan et al, 2009) and could be linked to resistance/susceptibility responses to G. cichoracearum in the mutants examined here. In line with this discussion, we note that treatment with the cellulose synthesis inhibitor isoxaben induces ectopic lignin accumulation in wild-type plants but not in det2-1 and noxy2-2 mutants (Supplemental Fig.…”

Population genomics of the eastern cottonwood (Populus deltoides)

“…In a genomewide association study, we recently conducted on the same P. deltoides population analyzed here (Fahrenkrog et al., 2017), a SNP present in this gene was positively associated with wood lignin content. Lignin is a polymer that increases rigidity and resistance of plant cell walls, playing an important role in the plant's defense against pathogens (Bhuiyan, Selvaraj, Wei, & King, 2009). This indicates that gene Potri.006G021900 could be involved in pathogen response through regulation of lignin biosynthesis.…”

Maize Homologs of CCoAOMT and HCT, Two Key Enzymes in Lignin Biosynthesis, Form Complexes with the NLR Rp1 Protein to Modulate the Defense Response

“…In parsley (Petroselinum crispum) suspension cells, the enzymatic activity of CCoAOMT rapidly increased after fungal elicitor treatment (Pakusch et al, 1989). Down-regulation of CCoAOMT in N. benthamiana results in higher susceptibility to Pseudomonas syringae pv tabaci (Senthil-Kumar and Mysore, 2010), and silencing of CCoAOMT in wheat (Triticum aestivum) compromises the defense against powdery mildew (Bhuiyan et al, 2009). An Arabidopsis CCoAOMT mutant line displayed increased disease symptoms (SenthilKumar et al, 2010).…”

“…These include lignin itself as well as many phytoalexins, phytoanticipins, and the hormone salicylic acid (SA; Dixon et al, 2002). Not surprisingly, many genes encoding enzymes in the phenylpropanoid pathway have been implicated in the plant defense response, including Phe ammonia-lyase, cinnamoyl-CoA reductase, cinnamyl-alcohol dehydrogenase, caffeic/5-hydroxyferulic acid O-methyltransferase, HCT, and CCoAOMT (Kawasaki et al, 2006;Bhuiyan et al, 2009;Gallego-Giraldo et al, 2011b;Zhao and Dixon, 2014).…”