15.1 Introduction
It is obvious that duckweeds have captured more
attention worldwide because of their special
advantages: rapid growth rate, predominantly
asexual reproduction, small growth space
requirement and floating growth. Appenroth
et al. (2015) pointed out that the physiological
basis of the attractiveness of duckweeds as
experimental organisms and for applications is
mainly the rapid vegetative growth rate of the 37
species of this family. Duckweed clones represented the fastest growth of all flowering plants
(Ziegler et al. 2015). The sensitivity to some
toxicants and enrichment capacity made duckweeds widely used in biomonitoring and bioremediation in contaminated water. Furthermore,
duckweeds have increasingly been considered as
bioenergy and food sources alternatively due to
their high biomass accumulation rate and nutrients content including carbohydrates and proteins as response to global resources and
environmental crisis (Leng et al. 1995; Anderson
et al. 2011; Qian et al. 2012; Xu et al. 2012; Zhao
et al. 2012). Because of the economic and scientific potential, research on duckweeds in various aspects such as, morphology structure (White
and Wise 1998; Lemon and Posluszny 2000),
nutrient analysis (Appenroth et al. 2017), bioremediation (Karmakar et al. 2016; Teles et al.
2017) and genetic information (Hoeck et al.
2015; Cao et al. 2016) has increased exponentially in recent 30 years (Appenroth et al. 2013).
In comparison with traditional breeding, plant
biotechnology has provided adequate opportunities for faster and directional introduction of
beneficial traits into plants (Giri and Laxmi 2000;
Sahrawat et al. 2003; Jones 2005). Duckweeds
have also benefited from plant biotechnology,
which has provided many potential for efficient
selection of diverse plant genotypes and targeted
modification of duckweeds. Introduction of
exogenous genes into plant genome mainly
contains the following processes: the introduction of genes into plant cells, regeneration of
transgenic cells, selection and regeneration of
transgenic plants. The conventional transformation methods include Agrobacterium-mediated,
microinjection, electroporation, microprojectile
bombardment, etc. Agrobacterium-mediated
method has been considered as the most natural
means because exogenous genes were integrated
into plant through intergeneric transfer mechanism along with the growth of plants (Jouanin
et al. 1993). Furthermore, this method has been
widely applied to various plant species for
obtaining stable transformation lines, due to their
precise integration of exogenous genes into the
plant genome and high stability (Dai et al. 2001).
The other direct transformation techniques utilizing protoplasts or tissues were efficient in the
regeneration of transiently transformed plant.
Transient transformation is a simple and rapid
technology compared with stable transformation.
When DNA is delivered into plant target cells,
only a small portion (if any) will integrate into the
host chromosomes. Transient expression does not
depend on chromosomal integration of the
heterologous DNA; therefore, analysis of gene
expression cannot be confused by position effects
(Jones et al. 2009). Expression of the heterologous
DNA can be detected 3 h after DNA-delivery
(Abel and Theologis 1994). It reaches a peak
between 18 and 48 h and persists for 10 days
(Werr and Lörz 1986; Abel and Theologis 1994).
Although it lasts only for a few days, transient
transformation occupies a useful niche in many
aspects such as functional genomics, recombinant
protein production, protein subcellular localization and protein–protein interactions, since it
allows proteins to be highly expressed and effects
to be seen in a short time (Gheysen et al. 1998).
Efficient methods for genetic transformation
into different duckweed species have evolved
significantly in last few years. Currently, both
stable and transient transformation protocols
have been successfully developed in some
duckweed species (Table 15.1). In this paper, the
corresponding work on the genetic transformation of duckweed species was reviewed.
144
J. Yang et al.
It is obvious that duckweeds have captured more
attention worldwide because of their special
advantages: rapid growth rate, predominantly
asexual reproduction, small growth space
requirement and floating growth. Appenroth
et al. (2015) pointed out that the physiological
basis of the attractiveness of duckweeds as
experimental organisms and for applications is
mainly the rapid vegetative growth rate of the 37
species of this family. Duckweed clones represented the fastest growth of all flowering plants
(Ziegler et al. 2015). The sensitivity to some
toxicants and enrichment capacity made duckweeds widely used in biomonitoring and bioremediation in contaminated water. Furthermore,
duckweeds have increasingly been considered as
bioenergy and food sources alternatively due to
their high biomass accumulation rate and nutrients content including carbohydrates and proteins as response to global resources and
environmental crisis (Leng et al. 1995; Anderson
et al. 2011; Qian et al. 2012; Xu et al. 2012; Zhao
et al. 2012). Because of the economic and scientific potential, research on duckweeds in various aspects such as, morphology structure (White
and Wise 1998; Lemon and Posluszny 2000),
nutrient analysis (Appenroth et al. 2017), bioremediation (Karmakar et al. 2016; Teles et al.
2017) and genetic information (Hoeck et al.
2015; Cao et al. 2016) has increased exponentially in recent 30 years (Appenroth et al. 2013).
In comparison with traditional breeding, plant
biotechnology has provided adequate opportunities for faster and directional introduction of
beneficial traits into plants (Giri and Laxmi 2000;
Sahrawat et al. 2003; Jones 2005). Duckweeds
have also benefited from plant biotechnology,
which has provided many potential for efficient
selection of diverse plant genotypes and targeted
modification of duckweeds. Introduction of
exogenous genes into plant genome mainly
contains the following processes: the introduction of genes into plant cells, regeneration of
transgenic cells, selection and regeneration of
transgenic plants. The conventional transformation methods include Agrobacterium-mediated,
microinjection, electroporation, microprojectile
bombardment, etc. Agrobacterium-mediated
method has been considered as the most natural
means because exogenous genes were integrated
into plant through intergeneric transfer mechanism along with the growth of plants (Jouanin
et al. 1993). Furthermore, this method has been
widely applied to various plant species for
obtaining stable transformation lines, due to their
precise integration of exogenous genes into the
plant genome and high stability (Dai et al. 2001).
The other direct transformation techniques utilizing protoplasts or tissues were efficient in the
regeneration of transiently transformed plant.
Transient transformation is a simple and rapid
technology compared with stable transformation.
When DNA is delivered into plant target cells,
only a small portion (if any) will integrate into the
host chromosomes. Transient expression does not
depend on chromosomal integration of the
heterologous DNA; therefore, analysis of gene
expression cannot be confused by position effects
(Jones et al. 2009). Expression of the heterologous
DNA can be detected 3 h after DNA-delivery
(Abel and Theologis 1994). It reaches a peak
between 18 and 48 h and persists for 10 days
(Werr and Lörz 1986; Abel and Theologis 1994).
Although it lasts only for a few days, transient
transformation occupies a useful niche in many
aspects such as functional genomics, recombinant
protein production, protein subcellular localization and protein–protein interactions, since it
allows proteins to be highly expressed and effects
to be seen in a short time (Gheysen et al. 1998).
Efficient methods for genetic transformation
into different duckweed species have evolved
significantly in last few years. Currently, both
stable and transient transformation protocols
have been successfully developed in some
duckweed species (Table 15.1). In this paper, the
corresponding work on the genetic transformation of duckweed species was reviewed.
144
J. Yang et al.