Environmental Engineering Reference
In-Depth Information
reported transformation frequency is low (0.09%) for hygromycin resistance, the coexpression fre-
quency of the reporter gene was 62.5%. With the development of this transformation system, a
platform is laid to make further improvements for transformation of sweet sorghum. This develop-
ment may pave the way for metabolic engineering of sugar metabolism in sweet sorghum. Genetic
modifications that will impart sweet sorghum resistance to biotic and abiotic stresses may also be
achieved with further refining of this protocol.
3.4.4 S witchgraSS
Switchgrass is a perennial high biomass grass native to the prairies of North America. It is identi-
fied by the U.S. Department of Energy (DOE) as one of the United States' promising energy crops
for many reasons. It is drought tolerant, high yielding, perennial, enhances soil and wildlife, can
be established from seed, and is adaptable to marginal lands (Bouton 2008). Several soil types
are tolerated, ranging from sands to heavy clays and pH levels of 5-7. Yields are approximately
10-25 Mg/ha per year (Yuan et al. 2008). Switchgrass is taxonomically divided into two groups:
lowland and upland. Lowland plants are considered coarse and tall with large biomass yields and
are found in wet regions with milder winters; upland plants are shorter, have a lower biomass
yield, and are found in drier and colder regions. Studies have shown two types of chloroplast
DNA, U and L, which show differences that can determine if the plant is an upland or lowland
plant (Bouton 2008).
There are a few published reports on genetic engineering of switchgrass (Richards et al. 2001;
Somleva et al. 2002, 2008; Xi et al. 2009; Li and Qu 2010). Richards et al. (2001) reported pro-
duction of transgenic switchgrass expressing GFP reporter gene. Somleva et al. (2002) generated
transgenic switchgrass expressing the bar gene, which confers resistance to the herbicide Basta.
More recently, Somleva et al. (2008) developed transgenic switchgrass producing polyhydroxy-
butyrate, a value-added co-product. Xi et al. (2009) demonstrated transformation of switchgrass
with a chimeric hygromycin phosphor-transferage gene. Li and Qu (2010) have developed a high-
throughput, Agrobacterium -mediated transformation system for switchgrass cv. Alamo. Using this
modified protocol, they have been able to transform switchgrass cv. Performer with 90% efficiency
and cv. Alamo and Colony with 50% efficiency. With the advancement in transformation protocols,
it is anticipated that other genes of interest to cellulosic biofuel production (e.g., genes controlling
cellulose metabolism, lignin metabolism) may be introduced to this important biofuel feedstock in
the near future.
3.4.5 m iScanthuS
Miscanthus is a high biomass, cold-tolerant, perennial grass easily propagated by rhizomes and has
the potential to be a contributor to ethanol production (Clifton-Brown et al. 2008). Originating in
East Asia, its natural range stretches from northeastern Siberia to the temperate area of Polynesia,
and toward central India. Needless to say, miscanthus thrives in a wide range of climates. Currently
Miscanthus spp . , specifically Miscanthus × giganteus , is being used in Europe as the main feed-
stock for biofuel. This hybrid species is sterile and requires vegetative propagation. Miscanthus has
shown better cold tolerance than switchgrass, possibly allowing for growth at high latitudes; it can
possibly use nitrogen better than switchgrass; and has a yield between 7 and 38 Mg/ha per year
(Yuan et al. 2008).
Although there are a couple of published reports on tissue culture of miscanthus (Holmes and
Petersen 1996; Kim et al. 2010b), there is only one report of genetic engineering of miscanthus.
Callus initiated from immature spikelets or germinating seeds was transformed using A. tume-
faciens . Selection was carried out using antibiotic G-418 with a npt II selectable marker and
plants were regenerated from callus (Engler and Chen 2009). It is anticipated that, with further
refining of transformation protocols, this important cellulosic ethanol biomass will be genetically
Search WWH ::




Custom Search