Lignin is the double-edged sword of biofuels: if you are making cellulosic ethanol, you want less lignin because it blocks the breakdown of cellulose. If you are using pyrolytic methods, you want more lignin because lignin contains more energy than cellulose.
Whether you wish to maximize or minimize lignin content, an understanding of lignin synthesis is essential and has proved elusive. Lignin is a key adaptation to life on land, as it strengthens plant cell walls thereby helping land plants stand upright and reinforcing the cell walls of the specialized water-conducting tubes that are another key adaptation to growth in terrestrial environments.
The lignin polymer is made up of a complex arrangement of subunits and its subunit composition differs among different species. For example, ferns and conifers have lignin composed mainly of p-hydroxyphenyl (H) and guaiacyl (G) lignin units. Flowering plants have H and G subunits, plus syringyl (S) subunits derived from sinapyl alcohol. Interestingly, S lignin is also found in some lycophytes, including the spikemoss Selaginella (photo). In research published this week in The Plant Cell, a team of researchers led by Clint Chapple of Purdue University showed that lignin synthesis proceeds along a different path in Selaginella. Their work centers on the characterization of the enzyme ferulate 5-hydroxylase (F5H); in flowering plants, this enzyme produces S lignin units from G lignin precursors. By comparing the Selaginella enzyme (Sm F5H) to the F5H from the model flowering plant Arabidopsis thaliana (At F5H), the authors found that Sm F5H could both catalyze the same reaction as At F5H and could also catalyze an additional reaction, acting on precursors of H lignin to form precursors to G and S lignin, and thereby bypassing four steps in angiosperm lignin synthesis. Indeed, transgenic expression of Sm F5H can restore normal lignin deposition to Arabidopsis plants with mutations in other enzymes of lignin biosynthesis. Interestingly, some combinations of transgenic Sm F5H and Arabidopsis lignin mutations produce lignin compositions likely not seen in nature, indicating that manipulation of this pathway can be used to engineer lignin composition. Moreover, since different lignin subunit compositions produce different lignin structural properties, this engineering may affect biomass characteristics such as digestibility. Author Clinton Chapple notes “It is exciting to realize that the study of plants so distantly related to crops can provide us with new tools to engineer plants that are of benefit to humans.”
This research also provides interesting insights on convergent evolution, the process whereby different evolutionary lineages arrive at similar adaptations, such as the independent evolution of wings for flight in bats and birds. Selaginella is part of one of the oldest divisions of vascular plants, resulting from an ancient split between the lycophytes and euphyllophytes (which include all modern seed plants). Similar to bat wings and bird wings, the synthesis of S lignin appears to have arisen independently in flowering plants and in lycophytes. Thus, this research provides both an interesting window on convergent evolution in plants and a potentially useful tool for engineering lignin synthesis.
This research was supported by the National Science Foundation, the U.S. Department of Energy office of Science, and the Life Sciences Research Foundation.
Jennifer Mach | EurekAlert!
New findings help to better calculate the oceans’ contribution to climate regulation
14.11.2018 | Jacobs University Bremen gGmbH
How algae and carbon fibers could sustainably reduce the athmospheric carbon dioxide concentration
14.11.2018 | Technische Universität München
Biochips have been developed at TU Wien (Vienna), on which tissue can be produced and examined. This allows supplying the tissue with different substances in a very controlled way.
Cultivating human cells in the Petri dish is not a big challenge today. Producing artificial tissue, however, permeated by fine blood vessels, is a much more...
Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.
In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...
On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.
When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure
Now, a team of Penn Engineers has demonstrated a new material they call "nanocardboard," an ultrathin equivalent of corrugated paper cardboard. A square...
Physicists at ETH Zurich demonstrate how errors that occur during the manipulation of quantum system can be monitored and corrected on the fly
The field of quantum computation has seen tremendous progress in recent years. Bit by bit, quantum devices start to challenge conventional computers, at least...
09.11.2018 | Event News
06.11.2018 | Event News
23.10.2018 | Event News
14.11.2018 | Materials Sciences
14.11.2018 | Health and Medicine
14.11.2018 | Life Sciences