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Title: Phylogenetic, molecular, and biochemical characterization of caffeic aicd O-methyltransferase (COMT) gene family in Brachypodium distachyon

Author
item WU, XIANTING - University Of California
item JU, JIAJIE - University Of California
item Bragg, Jennifer
item Vogel, John
item Anderson, Olin
item Gu, Yong

Submitted to: International Journal of Plant Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2012
Publication Date: 1/15/2013
Citation: Wu, X., Ju, J., Bragg, J.N., Vogel, J.P., Anderson, O.D., Gu, Y.Q. 2013. Phylogenetic, molecular, and biochemical characterization of caffeic aicd O-methyltransferase (COMT) gene family in Brachypodium distachyon. International Journal of Plant Genomics. doi.org/10.1155/2013/423189.

Interpretive Summary: The use of cellulosic biomass crops as a feedstock for the production of transportation fuel offers significant potential environmental and economic advantages. However, due to the difficulty in converting the sugars locked in cellulose and hemicellulose into fuel, our ability to use this renewable feedstock is limited. A deeper understanding of the genes that control cell wall biosynthesis and architecture may allow us to tailor the cell wall to be more amenable to conversion into biofuel. In this study, Caffeic acid O-methyltransferase (COMT), one of the important enzymes controlling lignin monomer production in plant cell wall synthesis was characterized in detail. Biochemical characterization on enzyme activity and substrate specificity showed that it has significant activity on a broad range of substrates with the highest preference for caffeic acid. The isolation and characterization of Brachypodium COMTs will permit us to develop an efficient system to analyze these enzymes in the lignin biosynthesis pathway through forward and reverse genetics approaches in this tractable model species.

Technical Abstract: Caffeic acid O-methyltransferase (COMT) is one of the important enzymes controlling lignin monomer production in plant cell wall synthesis. Analysis of the genome sequence of new grass model Brachypodium distachyon identified four COMT gene homologues, designated as BdCOMT1, BdCOMT2, BdCOMT3, and BdCOMT4. Phylogenetic analysis suggested that they belong to COMT gene family, whereas syntenic analysis through comparisons with rice and sorghum revealed that BdCOMT1 on Chr.3 is the orthologous copy of the COMT genes well characterized in other grass species. The other three COMT genes are unique to Brachypodium since orthologous copies are not found in the collinear regions of rice and sorghum genomes. Expression studies indicated that all four Brachypodium COMT genes are transcribed, but with distinct patterns of tissue specificity. Full-length cDNAs were cloned in-frame into the pQE-T7 expression vector for purification of recombinant Brachypodium COMT proteins. Biochemical characterization on enzyme activity and substrate specificity showed that BdCOMT1 has significant activity on a broad range of substrates with the highest preference for caffeic acid. The other three COMTs had low or no activity on these substrates, suggesting diversified evolution occurred on these duplicate genes that not only impacted on their pattern of expression, but also altered biochemical properties.