(219a) “Science Looks to Unlock Potential In the Undomesticated Tree Through Precise Genetic Breeding”

Scientific advances are unlocking ever more significant uses for the components of trees.  In addition to the wood, pulp for paper and wood for fire, increasing demands are being made of trees for fine grade cellulosic sugars that can be converted to biofuels, polyethylene and other compounds for industrial use. Yet the tree itself remains an undomesticated plant.  Far from its agricultural counterparts which have been bred for cold tolerance, drought resistance, improved yields and improved food quality, the tree has only been bred for a few generations and predominately to improve form for processing lumber.

ArborGen uses advance breeding techniques to shorten the time required to reach domesticated species for industrial purposes.  Varietal propagation allows us to replicate one species to improve consistency. Mass Controlled Pollination allows us to improve a line by controlling one parent in a breeding pair.  However, demands for wood cellulose are growing at a rate of acceleration that can never be matched at the conventional breeding level for a species that takes more than 20 years to mature.  ArborGen scientists use precision breeding techniques to look at specific ways of improving and domesticating trees for industrial uses.

One excellent example is a lignin-modified Eucalyptus species that has proven to release more than twice the usual amount of sugar, making it a promising option as a biomass feedstock for liquid fuel. The tree is being studied by National Renewable Energy Lab (NREL). Using plant biotechnology the modifications were made at two points in the lignin biosynthetic pathway, with the largest increase in sugar release coming from cinnamate-4-hydroxylase (C4H) down-regulation.  Although some “low recalcitrance” plant lines suffer from reduced growth, many of the C4H down-regulated lines from the E. grandis x E.  urophylla cross grow well.  C4H lines have an estimated biomass productivity of ten dry-tons per acre per year, with the potential to produce about 1,000 gallons of liquid biofuels per acre.

Scientists from NREL have characterized the C4H lines as containing half the lignin of the unmodified lines.  Using a high throughput sugar release assay developed at NREL (Selig et al, 2011 Biotech. Letters 1-7), the modified lines were found to release up to 99 percent of their sugars, up from 40 percent in the non-modified plants.  This result translates to an improvement of 150 percent, a dramatic demonstration of the impact of lowering recalcitrance.

Further work by NREL and ArborGen on these and similar lines will aim to understand exactly how the recalcitrance is lowered and how this knowledge can be used to develop healthy low recalcitrance lines in an array of species.