Submitted to: BioEnergy Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 3, 2010
Publication Date: June 1, 2011
Repository URL: http://hdl.handle.net/10113/49283
Citation: Saathoff, A.J., Tobias, C.M., Sattler, S.E., Haas, E.E., Twigg, P., Sarath, G. 2011. Switchgrass contains two cinnamyl alcohol dehydrogenases involved in lignin formation. BioEnergy Research. 4(2):120-133. Interpretive Summary: Switchgrass (Panicum virgatum L.) is a perennial polyploid grass with considerable potential as a bioenergy species. In this paper we have analyzed one of the key enzymes, cinnamyl alcohol dehydrogenase (CAD) that is involved in lignin biosynthesis. Our studies reveal that there is one dominant gene that codes for this activity. We have also detected two other related CAD genes in switchgrass. Our work will serve as a baseline for future studies on understanding cell wall quality parameters in novel switchgrass germplasm.
Technical Abstract: Switchgrass (Panicum virgatum L.) is a perennial polyploid grass with considerable potential as a bioenergy species. Many aspects of its biology and cell wall development are yet to be elucidated. Lignin content of cell walls is one of the key determinants of biomass quality and is a negative trait for conversion of biomass into liquid fuels. One of the key enzymes in lignin biosynthesis is cinnamyl alcohol dehydrogenase (CAD). In this study, we have shown that CAD activity and protein levels decrease minimally in developmentally distinct switchgrass internodes suggesting that lignification is a continuous process at all stages of tiller development. Thioacidolysis revealed that all lignin monomers continue to increase with increasing maturity of switchgrass internodes. 2-dimensional gel electrophoresis indicated that several spots immunologically detected as CAD were found in internode protein extracts. A RT-qPCR analysis of three CAD/CAD-like sequences indicated that transcripts coding for a specific switchgrass CAD (PviCAD1) were present in greater abundance than a closely related PviCAD2 sequence. Transcripts for a third CAD-like sequence (PviAroADH) were present at intermediate levels as compared to PviCAD1 and CAD2. We biochemically characterized recombinant PviCAD1 and showed that it had significant activity against both sinaplaldehyde and coniferaldehyde providing evidence that it was probably responsible for the dominant CAD activity in-situ. In contrast, the CAD-like PviAroADH appeared to be an enzyme unrelated to lignification based on phylogenetic and protein modeling data. These data indicate the existence of a signature motif that appears to distinguish bona-fide CADs from more distantly related alcohol dehydrogenases.