Landoltia commemorates Elias Landoltia for
his outstanding contributions to systematics and
biology of Lemnaceae. L. punctata possesses
2–7 roots per frond, perforating the prophyllum.
Its frond is ovate to lanceolate with 3–7 veins,
and a red dorsal surface is often observed. Unlike
Spirodela, Landoltia is turion-absent (Les and
Crawford 1999).
The most application field of L. punctata is
starch production. In 1970, Reid and Bieleski
reported that L. punctata accumulated starch
content to approximately 30% (dry weight) in
30 days cultivation on phosphorus-deficient
complete mineral nutrient medium. The starch
content was sharply increased to 75% (dry
weight) with the presence of glucose (1%) in the
medium (Reid and Bieleski 1970). In our previous studies, we evaluated various approaches,
like nutrient starvation, uniconazole supplementation, and heavy metal (cobalt and nickel) stress,
to induce starch accumulation by L. punctata
(Tao et al. 2013; Liu et al. 2015b; Guo et al.
2017). The three approaches evaluated induced
starch accumulation and resulted in approximately 50% (dry weight) of starch content in
10 days cultivation. Phytoremediation is another
important application field for L. punctata.
L. punctata is able to uptake nitrogen (N) and
phosphorus (P) from water very quickly, even
under relatively low N/P concentration. It is
widely used to purify wastewater and eutrophic
water bodies (Fang et al. 2007). Besides,
L. punctata is resistant to heavy metals to some
extent and is able to accumulate heavy metals
like cadmium, cobalt, nickel, lead, uranium, and
silver (Guo et al. 2017; Nie et al. 2016; Stegemeier et al. 2017; Tang et al. 2017; Fang et al.
2007). Also, it is reported that L. punctata is
potential for phytoremediation on petroleum
hydrocarbons (Ertekin et al. 2015). L. punctata is
rich in flavonoids (Wang et al. 2014) and is used
in traditional Chinese medicine. It is also
potential for pharmaceutical drugs.
To further release and improve the potential
applications, it is critical to interpret the physiological mechanism on how L. punctata response
to changing environment. General central dogma
states as “DNA makes RNA and RNA makes
protein”. RNA sequencing plays an important
role in understanding gene expression regulation,
and transcriptome analysis is able to reflect the
global regulation. With the decreasing cost of
next-generation sequencing, transcriptome analysis is accessible for individual laboratory and a
few duckweed transcriptome studies were carried
out in recent years (Table 12.1). Applying this
deep-sequencing technology will set framework
and stimulate novel potential of duckweeds. In
this chapter, we introduced the primary researches on L. punctata and its transcriptome analysis. This will give the readers insights into the
current status and future perspectives in researches and application potential of L. punctata.
12.2 Starch Production
and Transcriptome Analysis
L. punctata is a potential bioenergy crop with
high starch productivity and low lignin content.
Several transcriptome studies in L. punctata had
been carried out for understanding the mechanism of high starch content and low lignin content under abiotic stress.
The comparative transcriptome analysis was
conducted to reveal the mechanism of high starch
accumulation of L. punctata 0202 under nutrient
starvation. L. punctata 0202 was transferred from
nutrient-rich solution to distilled water and
sampled in time course. Physiological measurements revealed that the activity of the key
enzyme of starch biosynthesis, ADP-glucose
pyrophosphorylase (AGPase), as well as the
starch content increased continuously in
L. punctata 0202 under nutrient starvation condition. Samples harvested at 0, 2, and 24 h were
used for RNA-Seq, respectively. A comprehensive transcriptome, containing 74,797 contigs,
was obtained by a de novo assembly of the
RNA-Seq reads. Gene expression profiling
showed that transcripts encoding key enzymes
responsible for starch biosynthesis were
up-regulated. Inversely, the expression of transcripts encoding enzymes involved in starch
consumption and some photosynthesis-related
transcripts were down-regulated. Specifically,
126
Y. Fang et al.
his outstanding contributions to systematics and
biology of Lemnaceae. L. punctata possesses
2–7 roots per frond, perforating the prophyllum.
Its frond is ovate to lanceolate with 3–7 veins,
and a red dorsal surface is often observed. Unlike
Spirodela, Landoltia is turion-absent (Les and
Crawford 1999).
The most application field of L. punctata is
starch production. In 1970, Reid and Bieleski
reported that L. punctata accumulated starch
content to approximately 30% (dry weight) in
30 days cultivation on phosphorus-deficient
complete mineral nutrient medium. The starch
content was sharply increased to 75% (dry
weight) with the presence of glucose (1%) in the
medium (Reid and Bieleski 1970). In our previous studies, we evaluated various approaches,
like nutrient starvation, uniconazole supplementation, and heavy metal (cobalt and nickel) stress,
to induce starch accumulation by L. punctata
(Tao et al. 2013; Liu et al. 2015b; Guo et al.
2017). The three approaches evaluated induced
starch accumulation and resulted in approximately 50% (dry weight) of starch content in
10 days cultivation. Phytoremediation is another
important application field for L. punctata.
L. punctata is able to uptake nitrogen (N) and
phosphorus (P) from water very quickly, even
under relatively low N/P concentration. It is
widely used to purify wastewater and eutrophic
water bodies (Fang et al. 2007). Besides,
L. punctata is resistant to heavy metals to some
extent and is able to accumulate heavy metals
like cadmium, cobalt, nickel, lead, uranium, and
silver (Guo et al. 2017; Nie et al. 2016; Stegemeier et al. 2017; Tang et al. 2017; Fang et al.
2007). Also, it is reported that L. punctata is
potential for phytoremediation on petroleum
hydrocarbons (Ertekin et al. 2015). L. punctata is
rich in flavonoids (Wang et al. 2014) and is used
in traditional Chinese medicine. It is also
potential for pharmaceutical drugs.
To further release and improve the potential
applications, it is critical to interpret the physiological mechanism on how L. punctata response
to changing environment. General central dogma
states as “DNA makes RNA and RNA makes
protein”. RNA sequencing plays an important
role in understanding gene expression regulation,
and transcriptome analysis is able to reflect the
global regulation. With the decreasing cost of
next-generation sequencing, transcriptome analysis is accessible for individual laboratory and a
few duckweed transcriptome studies were carried
out in recent years (Table 12.1). Applying this
deep-sequencing technology will set framework
and stimulate novel potential of duckweeds. In
this chapter, we introduced the primary researches on L. punctata and its transcriptome analysis. This will give the readers insights into the
current status and future perspectives in researches and application potential of L. punctata.
12.2 Starch Production
and Transcriptome Analysis
L. punctata is a potential bioenergy crop with
high starch productivity and low lignin content.
Several transcriptome studies in L. punctata had
been carried out for understanding the mechanism of high starch content and low lignin content under abiotic stress.
The comparative transcriptome analysis was
conducted to reveal the mechanism of high starch
accumulation of L. punctata 0202 under nutrient
starvation. L. punctata 0202 was transferred from
nutrient-rich solution to distilled water and
sampled in time course. Physiological measurements revealed that the activity of the key
enzyme of starch biosynthesis, ADP-glucose
pyrophosphorylase (AGPase), as well as the
starch content increased continuously in
L. punctata 0202 under nutrient starvation condition. Samples harvested at 0, 2, and 24 h were
used for RNA-Seq, respectively. A comprehensive transcriptome, containing 74,797 contigs,
was obtained by a de novo assembly of the
RNA-Seq reads. Gene expression profiling
showed that transcripts encoding key enzymes
responsible for starch biosynthesis were
up-regulated. Inversely, the expression of transcripts encoding enzymes involved in starch
consumption and some photosynthesis-related
transcripts were down-regulated. Specifically,
126
Y. Fang et al.