cellulose are considered as a promising feedstock
for biofuels as well as potential in wastewater
treatment.
15.4.3 Bioreactor
Recently, plant bioreactor has emerged as an
attractive area for its low cost, product safety and
easy scale-up (Tiwari et al. 2009). Variety of
products including vaccine antigens, medical
diagnostics proteins, industrial and pharmaceutical proteins, nutritional supplements like minerals, vitamins, carbohydrates and biopolymers
have been attempted to express in plant bioreactors based on transgenic plants systems (Sharma
and Sharma 2009). As a safe and cost-effective
alternative expression platform, plant bioreactor
was of great importance in the area of animal and
human health and diagnostics (Ma et al. 2005;
Boehm 2007). Plant systems based on transgenic
food crops such as tobacco, tomato, rice, potato,
maize, carrot and soybean have already served as
efficient bioreactors for expressing recombinant
products as well as other non-food and/or
non-crops (Cox et al. 2006; Tiwari et al. 2009;
Rybicki 2010; Tremblay et al. 2010).
Selection of the host species is a critical step
for the establishment of efficient bioreactor.
Many factors such as the life cycle of plant
species, reproductive rate, biomass yield and
scale-up costs can affect the choice of suitable
host. Therefore, duckweed species were ideal as
plant bioreactor for their aquatic and short life
cycle, rapid asexual reproduction, high biomass
and protein yield, easy harvesting and cultivation, small living space, and easy to transform
(Landolt 1986). Duckweed expression systems
indeed promote rapid expansion of transgenic
plants, secretion of recombinant proteins and
high protein yield (Cox et al. 2006). The
endoglucanase E1 gene from Acidothermus cellulolyticus has been expressed in transgenic L.
minor. The duckweed-expressed enzyme was
biologically active with expression level up to
0.24% of total soluble protein demonstrating
possibilities for the expression of cellulolytic
enzymes in transgenic duckweeds (Sun et al.
2007). Various proteins, such as mAbs, aprotinin, TNFa have also been expressed at high
levels in Lemna and Spirodela species, which
enables protein production by duckweed bioreactor in a robust and controllable format (Cox
et al. 2006; Rival et al. 2008; Balaji et al. 2015).
Antigen protein porcine epidemic diarrhea
virus (PEDV) expressed in transgenic L. minor
was the first report on the expression of antigen
vaccine against an animal infectious disease in
duckweeds (Ko et al. 2011). A synthetic
hemagglutinin (HA) gene from the highly
pathogenic avian influenza (HPAI) virus
A/chicken/Indonesia/7/2003 (H5N1) (Indo/03)
was successfully expressed in L. minor (rLemnaHA) (Bertran et al. 2015). The transgenic
duckweed derived HA produced high-quality
antigen for an injectable vaccine against
H5N1 HPAI viruses. S. polyrhiza, capable of
growth and good biomass production, was also
used to express HA1 gene encoding hemagglutinin antigen of H5N1 virus for further generation of vaccine (Thu et al. 2015). In addition, the
M2e peptide was expressed in nucleartransformed duckweed plants with no noticeable impact on the plant morphology or growth
rate, and the accumulation reached to 40 µg/g
FW which was equivalent to levels obtained in
transient virus-based systems (Firsov et al. 2015).
The development of safe and effective vaccines
against highly pathogenic influenza A virus
subtype H5N1 has been recognized as an
essential approach to decrease risk of transmission in poultry and humans, Furthermore, it
opens the way to develop an edible plant vaccine
against avian influenza virus (Bertran et al. 2015;
Firsov et al. 2015).
15.5 Conclusion and Future
Perspectives
Although protocols for gene transformation have
been established in some duckweed species,
inadequacies are still present. Low-transformation
efficiency and long-period consumption were the
152
J. Yang et al.
for biofuels as well as potential in wastewater
treatment.
15.4.3 Bioreactor
Recently, plant bioreactor has emerged as an
attractive area for its low cost, product safety and
easy scale-up (Tiwari et al. 2009). Variety of
products including vaccine antigens, medical
diagnostics proteins, industrial and pharmaceutical proteins, nutritional supplements like minerals, vitamins, carbohydrates and biopolymers
have been attempted to express in plant bioreactors based on transgenic plants systems (Sharma
and Sharma 2009). As a safe and cost-effective
alternative expression platform, plant bioreactor
was of great importance in the area of animal and
human health and diagnostics (Ma et al. 2005;
Boehm 2007). Plant systems based on transgenic
food crops such as tobacco, tomato, rice, potato,
maize, carrot and soybean have already served as
efficient bioreactors for expressing recombinant
products as well as other non-food and/or
non-crops (Cox et al. 2006; Tiwari et al. 2009;
Rybicki 2010; Tremblay et al. 2010).
Selection of the host species is a critical step
for the establishment of efficient bioreactor.
Many factors such as the life cycle of plant
species, reproductive rate, biomass yield and
scale-up costs can affect the choice of suitable
host. Therefore, duckweed species were ideal as
plant bioreactor for their aquatic and short life
cycle, rapid asexual reproduction, high biomass
and protein yield, easy harvesting and cultivation, small living space, and easy to transform
(Landolt 1986). Duckweed expression systems
indeed promote rapid expansion of transgenic
plants, secretion of recombinant proteins and
high protein yield (Cox et al. 2006). The
endoglucanase E1 gene from Acidothermus cellulolyticus has been expressed in transgenic L.
minor. The duckweed-expressed enzyme was
biologically active with expression level up to
0.24% of total soluble protein demonstrating
possibilities for the expression of cellulolytic
enzymes in transgenic duckweeds (Sun et al.
2007). Various proteins, such as mAbs, aprotinin, TNFa have also been expressed at high
levels in Lemna and Spirodela species, which
enables protein production by duckweed bioreactor in a robust and controllable format (Cox
et al. 2006; Rival et al. 2008; Balaji et al. 2015).
Antigen protein porcine epidemic diarrhea
virus (PEDV) expressed in transgenic L. minor
was the first report on the expression of antigen
vaccine against an animal infectious disease in
duckweeds (Ko et al. 2011). A synthetic
hemagglutinin (HA) gene from the highly
pathogenic avian influenza (HPAI) virus
A/chicken/Indonesia/7/2003 (H5N1) (Indo/03)
was successfully expressed in L. minor (rLemnaHA) (Bertran et al. 2015). The transgenic
duckweed derived HA produced high-quality
antigen for an injectable vaccine against
H5N1 HPAI viruses. S. polyrhiza, capable of
growth and good biomass production, was also
used to express HA1 gene encoding hemagglutinin antigen of H5N1 virus for further generation of vaccine (Thu et al. 2015). In addition, the
M2e peptide was expressed in nucleartransformed duckweed plants with no noticeable impact on the plant morphology or growth
rate, and the accumulation reached to 40 µg/g
FW which was equivalent to levels obtained in
transient virus-based systems (Firsov et al. 2015).
The development of safe and effective vaccines
against highly pathogenic influenza A virus
subtype H5N1 has been recognized as an
essential approach to decrease risk of transmission in poultry and humans, Furthermore, it
opens the way to develop an edible plant vaccine
against avian influenza virus (Bertran et al. 2015;
Firsov et al. 2015).
15.5 Conclusion and Future
Perspectives
Although protocols for gene transformation have
been established in some duckweed species,
inadequacies are still present. Low-transformation
efficiency and long-period consumption were the
152
J. Yang et al.