Wood Formation Studies in Poplar – Genetic
Tools for Carbon Sequestration and Biofuels
Research
Andrew Groover
USDA Forest Service
Institute of Forest Genetics
Davis CA
http://www.fs.fed.us/psw/programs/ifg/
The Genus Populus
(poplars, cottonwoods, and aspens)
• Modest genome size
•
Clonal propagation and transformation
• Many interfertile, diverse species
• Relatively short generation times
• Fast growing
• Commercially grown
• Ecological and environmental
significance
Poplars as Cellulosic Biofuels
Feedstock
•
No direct competition with food
production.
•
Provides secondary benefits.
– Wildlife, soil, water quality.
•
Perennial growth gives greater
yields.
•
Optional harvest times, ease of
storage and transport.
•
Lower intensity agriculture with
more favorable net carbon.
– Fewer mechanical
treatments
– Little or no fertilizer
– Less herbicide
Native, non-Invasive Poplars
P. tremuloides
P. fremontii
P. trichocarpa
Images from USDA Plants database
Populus Genome
The JGI Genome Portal
http://genome.jgi-psf.org/
Multiple Benefits
• Same genomic tools
developed for
biofuels research in
Populus can be used
for conservation and
management.
• Mitigating impacts
of climate change on
forests.
Wood Formation is a Key Biological Process
Underlying Biofuels and Carbon Sequestration
•Maintenance of meristematic stem
cells in vascular cambium.
•Radial patterning of tissues.
•Differentiation of specialized cell
types.
Transcription Factors that Regulate the
Expression of Other Genes During Wood
Formation
•
How are cambium cells
specified and maintained in a
meristematic state?
– Class I KNOX
•
How are secondary vascular
tissues patterned and
partitioned?
– Class III HD ZIPs
Determining the Function of Genes
• Overexpress or “knock down”
expression of gene of
interest.
• Examine phenotype of
resulting plants
• Infer function based on
phenotypes
Wild Type Control
35S:ARK1
ARK1 Overexpression
Inhibits Cell
Differentiation and
Lignification
• Delays appearance of lignified,
differentiated cell types in
secondary vascular tissues.
• Erratic cambium divisions, or
daughter cell differentiation or
recruitment problems.
lub
le*
Wild Type
22.0
Ac
id
So
Ac
id
Total Lignin
ins
olu
ble
*
Lignin S/G Ratios are
Altered in Plants
Overexpressing ARK1
35S:ARK1
21.0
5.6
2.9
*mg/100mg
S/G Lignin Ratio
Wild Type
1
:
2
35S:ARK1
1
:
1
35S:ARK2 Has an Wider Cambium Region, and
Delayed Cell Differentiation
Wild Type
35S:ARK2
lub
le*
So
Ac
id
Ac
id
Total Lignin
ins
olu
ble
*
Lignification is
Reduced in
35S:ARK2
Wild Type
18.9
2.0
35S:ARK2
14.3
0.9
*mg/100mg
S/G Lignin Ratio
Wild Type
1
:
2
35S:ARK2
1
:
2
“Double” Cambium in miRNA-Resistant Poplar
REVOLUTA Stems
Cell & Tissue
Differentiation
Regulation of Meristem Maintenance and
Polarity in Secondary Vasculature
Cambium
Maintenance
ARK2
ARK1
ClassIII
HD Zips
Kanadis?
Phloem
Xylem
miRNA
Image from Dr David Webb
HIGH LD
LOW LD
H=40
H=50
H=60
H=60
H=70
H=70
H=90
H=90
H=100
H=110
Association Mapping of Genes Controlling
Traits of Interest
A
A
A
A
A
C
C
C
C
C
G
G
T
T
T
G
T
T
G
G
A
A
A
A
A
C
C
C
C
C
G
G
T
T
T
G
T
T
G
G
Identifying Genes Regulating Wood Properties
of Structural Roots
•Identify naturally occurring alleles
influencing wood properties in roots
•Compare wood properties and gene
expression in roots versus stems
Beyond the Basic
• Translating basic
genetic research into
applications.
Groover (2007) Will Genomics Guide a
Greener Forest Biotech? TIPS
Thanks!
Institute of Forest Genetics
Juan Du
Gayle Dupper
Annie Mix
Cecilia Osorio
Marcel Robischon
University British Columbia
Shawn Mansfield
Oakridge National Lab
Jerry Tuskan
University of W Virginia
Steve DiFazio
Purdue
Rick Meilan