Madhavi Bhatia,NIPER Guwahati
Wheat is an important source of human protein and mineral elements, it is also considered a major staple crop worldwide. Wheat production is mainly affected by one of the destructive diseases Fusarium head blight (FHB) also known as scab, caused by Fusarium graminearum (Fg). This disease results in huge wheat loss and imposition of substantial health threats in both humans and livestock animals due to DON toxin.
The cell wall of the plant is mainly composed of polysaccharides, phenolic compounds and proteins. The cell wall of the plant has the ability to resist the invasion of pathogens in the plant. In some studies, it was found that pectin methylesterase PME-1 and β-1,3-glucanase (Glu-1) could be considered the main causative genes of FHB resistance in wheat. These genes are involved in cell wall metabolism and regulate non-specific lipid transfer protein (nsLTP-1). Lignin is the second most abundant component present in the cell wall and involved in basal disease resistance in plants. In some studies, it was found that lignin is accumulated rapidly in the ear cell wall of both resistant and susceptible wheat spikes during Fusarium culmorum infection, but the content of lignin in resistant spikes was significantly higher than in susceptible spikes. Integrated metabolo-transcriptomics revealed that CAD (cinnamyl alcohol dehydrogenase) might be the putative resistance gene localized within the QTL-Fhb2 region, which is a crucial gene for lignin biosynthesis.
O-Methyltransferases (OMTs) enzyme play a crucial role in regulating the secondary metabolic processes which are involved in lignin biosynthesis. OMTs are classified into 2 types, caffeic acid O-methyltransferase (COMT) and caffeoyl-coenzyme A O-methyltransferase (CCoAOMT), of which COMT controls the S unit pathway and CCoAOMT affects the S and G unit pathways. COMT catalyze O-methylation at the 5-position of the aromatic ring while CCoAOMT catalyzes the 3 positions of the aromatic ring. The hydroxylation and methylation steps play a key role in determining the lignin composition and the S/G ratio is a major determinant of lignin quality.
Lignin is the main component of the cell wall it is also involved in the response to abiotic and biotic stresses. The characteristics of the caffeoyl-coenzyme A O-methyltransferase gene involved in the lignin synthesis pathway were analyzed in Arabidopsis, sorghum, and other plants. In the study, 21 caffeoyl-coenzyme A O-methyltransferases in wheat at genome level were identified. Based on RNA-seq samples, the expression levels of these wheat CCoAOMT genes in the tissues were analyzed, 7 TaC-CoAOMTs showed significant up-regulation of gene-expression after Fg treatment compared to resistant and susceptible variety. This suggests that TaC-CoAOMT play an important role in response to FHB. Cis-regulatory elements in the gene can regulate gene expression levels by binding to corresponding transcription factors, and this might determine the specific expression patterns in different tissue and stresses. The up-regulated TaC-CoAOMT containing CGTCA-motif and TGACG-motif might play a crucial role in regulating FHB tolerance through MeJA mediation. Micro-RNAs like miR167a mediates auxin signalling to respond to biotic stresses in tomatoes and miR1119 regulate expression of actin under stress conditions and activate plant defence signalling pathway in barley. Thus, it was hypothesized that these 2 miRNAs also play the regulatory role in the response to Fg infection by controlling the expression of CCoAOMT genes in wheat.
Thus, characterization of the CCoAMOT family in wheat will help in the development of potential targets for further functional analysis. It also revealed the mechanism of lignin biosynthesis and its role in FHB tolerance in wheat.
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Source-Yang, G., Pan, W., Zhang, R. et al. Genome-wide identification and characterization of caffeoyl-coenzyme A O-methyltransferase genes related to the Fusarium head blight response in wheat. BMC Genomics 22, 504 (2021). https://doi.org/10.1186/s12864-021-07849-y
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About the author: Madhavi Bhatia is currently pursuing a Master of Science in Pharmaceutical Biotechnology from NIPER, Guwahati. Her area of interest lies in understanding the role of gene mutation in the development of various diseases and developing treatments for such diseases.
Some of her publications at bioxone are-
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