Plant Cell Walls - an obvious target for synthetic biology
Talk by: Professor Henrik V. Scheller
Senior scientist at Lawrence Berkeley National Laboratory.
Adjunct Professor at Department of Plant & Microbial Biology, University of California Berkeley
Adjunt Professor at Department of Plant Biology, University of Copenhagen
Plant biomass for bioenergy purposes is composed largely of secondary cell walls, about a 25% of which is lignin and 35% of which are hemicelluloses. Lignin is a major factor in the recalcitrance of plant biomass to saccharification, and therefore plants with less lignin would be better feedstocks for biorefinery. In angiosperms, xylans are the principal hemicelluloses in secondary walls. A decreased xylan content in bioenergy crops is desirable because of the greater ease of fermenting hexoses compared to the pentoses that make up the xylans. However, both lignin and xylans have important roles in the plant, and their biosynthesis cannot simply be blocked without adverse effects on plant growth. In general lignin and xylan deficient mutants have poor growth properties, exhibiting a typical irregular xylem phenotype with collapsed vessels.
The Feedstocks Team at JBEI has developed methods to spatially and temporally fine-tune the deposition of lignin and xylan, and using specific transcription factors we have generated transgenic Arabidopsis plants where lignin and xylan is synthesized normally in vessels but not in interfascicular fibers. These plants exhibit normal growth and development. In addition we have developed a method of employing an artificial positive feedback loop that enhances transcriptional activity in a tissue-specific manner and allows generation of plants with increased density. Finally, we have developed methods to alter the composition of xylan and lignin that makes the plant biomass easier to deconstruct without affecting the content of the polymers. Our results comprise synthetic biology methods to generate bioenergy crops with improved properties for saccharification and production of more easily fermentable sugars.
The principles for using plant synthetic biology to engineer improved bioenergy plants are not limited to this goal. The same approaches can be used to engineer plants with improved agronomic properties, e.g. drought resistance, or for production of specific high-value compounds in plants.