12.3 Heavy Metal Accumulation
and Transcriptome Analysis
Except for transcriptome analysis for starch
accumulation, the gene expression response to
cadmium stress in L. punctata 6001 was analyzed
via RNA-Seq technique by Xu et al. L. punctata
6001, which is considered a promising candidate
for Cd phytoremediation, was isolated by largescale screening of over 200 duckweed clones. To
understand the molecular mechanisms of Cd
hyperaccumulation, a comprehensive transcriptome analysis was performed by RNA-Seq for
samples treated with 20 lM CdCl 2 for 0, 1, 3, and
6 days. Xu et al. revealed that genes involved in
DNA repair acted as an early response to Cd, and
RNA and protein metabolism would be likely to
respond as well. Furthermore, the carbohydrate
metabolic flux tended to be modulated in
response to Cd stress. Up-regulated genes
involved in sulfur and reactive oxygen species
(ROS) metabolism might contribute to Cd tolerance. Vacuolar sequestration most likely played
an important role in Cd detoxification in L.
punctata 6001. The novel findings provided
important clues for molecular-assisted screening
and breeding of Cd hyper-accumulating cultivars
for phytoremediation (Xu et al. 2018).
12.4 Flavonoids Accumulation
and Transcriptome Analysis
Flavonoids belong to phenolic compounds and
are widely existed secondary metabolites in
plants. It can be potentially exploited in the food
and drug. The flavonoid content of duckweed can
reach up to approximately 5.56%, and at least, 20
flavonoid compounds were found in duckweed
(Tao et al. 2017).
Nutrient starvation also triggers high flavonoid accumulation in L. punctata 0202. A combined omics study was performed to investigate
the biosynthesis of flavonoid and the metabolic
flux changes in L. punctata 0202 grown in different culture media. To understand the global
flavonoid and starch metabolite-related molecular response to nutrient starvation, L. punctata
0202 was cultivated in nutrient starvation, uniconazole treatment, and full nutrient, respectively. RNA-Seq analysis for three groups
sample was carried out, and the proteome data
obtained from iTRAQ-LC-MS/MS technology of
previous studies was re-analyzed using the new
transcriptome data as a reference database. The
abundance of the most detected flavonoid-related
proteins, including the phenylalanine ammonialyase (PAL), cinnamate 4-hydroxylase (C4H),
4-hydroxycinnamoyl-CoA
ligase
(4CL),
chalcone synthase (CHS), chalcone isomerase
(CHI), flavanone 3-hydroxylase (F3H), and
anthocyanidin synthase (ANS) were detected to
be improved in L. punctata 0202 when grown in
distilled water. The proteome data was consistent
with the transcriptome data in this study. Flavonoid content was measured, and purple coloration accumulation which is regarded as
anthocyanin was observed on the dorsal fronds.
The metabolome and morphology further verified the results of transcriptome and proteome
analysis (Tao et al. 2017).
12.5 Other Transcriptomes Analysis
Several transcriptome studies in other duckweed
species were also reported currently. Lemna
minor can grow well in the high NH 4
+ environment but to some extent can also suffer toxic
effects. To study the toxicity and tolerance of
NH 4
+
, the transcriptome study using RNA-Seq
was reported in L. minor. The L. minor was
cultured in the Hoagland solution of control and
treated with 84 mg/L NH 4
+ and 840 mg/L NH 4
+
.
RNA-Seq generated 6.62 G nucleotides from the
three distinct libraries. Bioinformatic analysis
identified 70,728 unigenes and 14,207 differentially expressed genes (DEGs), most of which
were down-regulated under NH 4
+ toxicity. Lignin biosynthesis-related genes in the phenylpropanoid
biosynthesis
pathway
were
up-regulated to enhance NH 4
+ toxicity resistance. The accumulation of ROS induced by
NH 4
+ toxicity can cause oxidative damage leading to cell death in L. minor. The antioxidant
enzyme system was also activated to scavenge
12 The Transcriptome in Landoltia punctata
129
and Transcriptome Analysis
Except for transcriptome analysis for starch
accumulation, the gene expression response to
cadmium stress in L. punctata 6001 was analyzed
via RNA-Seq technique by Xu et al. L. punctata
6001, which is considered a promising candidate
for Cd phytoremediation, was isolated by largescale screening of over 200 duckweed clones. To
understand the molecular mechanisms of Cd
hyperaccumulation, a comprehensive transcriptome analysis was performed by RNA-Seq for
samples treated with 20 lM CdCl 2 for 0, 1, 3, and
6 days. Xu et al. revealed that genes involved in
DNA repair acted as an early response to Cd, and
RNA and protein metabolism would be likely to
respond as well. Furthermore, the carbohydrate
metabolic flux tended to be modulated in
response to Cd stress. Up-regulated genes
involved in sulfur and reactive oxygen species
(ROS) metabolism might contribute to Cd tolerance. Vacuolar sequestration most likely played
an important role in Cd detoxification in L.
punctata 6001. The novel findings provided
important clues for molecular-assisted screening
and breeding of Cd hyper-accumulating cultivars
for phytoremediation (Xu et al. 2018).
12.4 Flavonoids Accumulation
and Transcriptome Analysis
Flavonoids belong to phenolic compounds and
are widely existed secondary metabolites in
plants. It can be potentially exploited in the food
and drug. The flavonoid content of duckweed can
reach up to approximately 5.56%, and at least, 20
flavonoid compounds were found in duckweed
(Tao et al. 2017).
Nutrient starvation also triggers high flavonoid accumulation in L. punctata 0202. A combined omics study was performed to investigate
the biosynthesis of flavonoid and the metabolic
flux changes in L. punctata 0202 grown in different culture media. To understand the global
flavonoid and starch metabolite-related molecular response to nutrient starvation, L. punctata
0202 was cultivated in nutrient starvation, uniconazole treatment, and full nutrient, respectively. RNA-Seq analysis for three groups
sample was carried out, and the proteome data
obtained from iTRAQ-LC-MS/MS technology of
previous studies was re-analyzed using the new
transcriptome data as a reference database. The
abundance of the most detected flavonoid-related
proteins, including the phenylalanine ammonialyase (PAL), cinnamate 4-hydroxylase (C4H),
4-hydroxycinnamoyl-CoA
ligase
(4CL),
chalcone synthase (CHS), chalcone isomerase
(CHI), flavanone 3-hydroxylase (F3H), and
anthocyanidin synthase (ANS) were detected to
be improved in L. punctata 0202 when grown in
distilled water. The proteome data was consistent
with the transcriptome data in this study. Flavonoid content was measured, and purple coloration accumulation which is regarded as
anthocyanin was observed on the dorsal fronds.
The metabolome and morphology further verified the results of transcriptome and proteome
analysis (Tao et al. 2017).
12.5 Other Transcriptomes Analysis
Several transcriptome studies in other duckweed
species were also reported currently. Lemna
minor can grow well in the high NH 4
+ environment but to some extent can also suffer toxic
effects. To study the toxicity and tolerance of
NH 4
+
, the transcriptome study using RNA-Seq
was reported in L. minor. The L. minor was
cultured in the Hoagland solution of control and
treated with 84 mg/L NH 4
+ and 840 mg/L NH 4
+
.
RNA-Seq generated 6.62 G nucleotides from the
three distinct libraries. Bioinformatic analysis
identified 70,728 unigenes and 14,207 differentially expressed genes (DEGs), most of which
were down-regulated under NH 4
+ toxicity. Lignin biosynthesis-related genes in the phenylpropanoid
biosynthesis
pathway
were
up-regulated to enhance NH 4
+ toxicity resistance. The accumulation of ROS induced by
NH 4
+ toxicity can cause oxidative damage leading to cell death in L. minor. The antioxidant
enzyme system was also activated to scavenge
12 The Transcriptome in Landoltia punctata
129