solution for 3 days under stable condition were
transferred into the same medium for an additional 10 days, but with uniconazole treatment in
the homogeneous condition, samples were harvested at 13 time points (0, 1, 2, 3, 5, 7, 12, 24,
48, 72, 120, 168, and 240 h) in time course for
composition characterization and enzymatic
activity assay in three biological replicates. Five
time point samples (0, 2, 5, 72, and 240 h) were
used for iTRAQ proteomic analysis. A total of
3327 proteins were identified. Among these
identified proteins, a large number of enzymes
involved in endogenous hormone synthetic and
starch metabolic pathways were affected. Notably, most of the enzymes involved in abscisic
acid (ABA) biosynthesis showed up-regulated
expression, which was consistent with the content variation. The increased endogenous ABA
may up-regulate expression of ADP-glucose
pyrophosphorylase to promote starch biosynthesis. Importantly, the up-regulated expression
levels of several key enzymes in the starch
biosynthetic pathway supported the enzymatic
assay results and may explain why there is
increased starch accumulation (Huang et al.
2015).
14.3 Flavonoids, Anthocyanin,
Lignin Biosynthesis,
and Proteomics in Landoltia
punctata
The iTRAQ data described above was
re-analyzed for flavonoid, anthocyanin, and lignin biosynthesis in phenylalanine metabolic
networks based on another transcriptome as a
new reference duckweed protein database
described by Tao (Tao et al. 2017). The expression level of key enzymes that are responsible for
flavonoid biosynthesis, such as phenylalanine
ammonia-lyase (PAL), cinnamate 4-hydroxylase
(C4H), 4-hydroxycinnamoyl-CoA ligase (4CL),
chalcone synthase (CHS), chalcone isomerase
(CHI), flavanone 3-hydroxylase (F3H), and
anthocyanidin synthase (ANS), was improved,
and the anthocyanin biosynthesis branch-related
enzymes such as F3H, dihydroflavonol
4-reductase (DFR) and ANS expression were
also increased under nutrient starvation in L.
punctata 0202 based on the result of re-analysis
for iTRAQ data, but PAL, C4H, and 4CL were
suppressed immediately by uniconazole treatment. However, almost all the key enzymes of
lignin biosynthetic branch in phenylalanine
metabolic network and 25 laccases assembled by
de novo RNA-Seq were not detected by
re-analysis for iTRAQ data in duckweed under
nutrient starvation and uniconazole treatment.
This study supported previous omics research
that the nutrient starvation treatment could
improve the starch and flavonoid content simultaneously (Tao et al. 2013; Huang et al. 2014)
and suggested that uniconazole treatment could
induce starch accumulation and suppress the
flavonoid content in duckweed (Tao et al. 2017).
14.4 Conclusion
Proteins are the direct undertakers of gene
function. The high-throughput proteomic method
facilitated our understanding of high starch
accumulation mechanism by duckweed at proteome level. Also, it showed powerful in studying mechanism elucidation. However, few
attention was paid to proteome analysis of
duckweed. We encourage more researchers to
focus on this field and thus promote our deepened understanding and wide application of
duckweed.
References
Angel TE, Aryal UK, Hengel SM et al (2012) Mass
spectrometry-based proteomics: existing capabilities
and future directions. Chem Soc Rev 41(10):3912–
3928. https://doi.org/10.1039/c2cs15331a
Chen L, Yu C, Ma Y et al (2016) Insights into the
structural and physicochemical properties of small
granular starches from two hydrophyte duckweeds,
Spirodela oligorrhiza and Lemna minor. Carbohydr
Res 435:208–214. https://doi.org/10.1016/j.carres.
2016.10.010
140
Y. Fang et al.
transferred into the same medium for an additional 10 days, but with uniconazole treatment in
the homogeneous condition, samples were harvested at 13 time points (0, 1, 2, 3, 5, 7, 12, 24,
48, 72, 120, 168, and 240 h) in time course for
composition characterization and enzymatic
activity assay in three biological replicates. Five
time point samples (0, 2, 5, 72, and 240 h) were
used for iTRAQ proteomic analysis. A total of
3327 proteins were identified. Among these
identified proteins, a large number of enzymes
involved in endogenous hormone synthetic and
starch metabolic pathways were affected. Notably, most of the enzymes involved in abscisic
acid (ABA) biosynthesis showed up-regulated
expression, which was consistent with the content variation. The increased endogenous ABA
may up-regulate expression of ADP-glucose
pyrophosphorylase to promote starch biosynthesis. Importantly, the up-regulated expression
levels of several key enzymes in the starch
biosynthetic pathway supported the enzymatic
assay results and may explain why there is
increased starch accumulation (Huang et al.
2015).
14.3 Flavonoids, Anthocyanin,
Lignin Biosynthesis,
and Proteomics in Landoltia
punctata
The iTRAQ data described above was
re-analyzed for flavonoid, anthocyanin, and lignin biosynthesis in phenylalanine metabolic
networks based on another transcriptome as a
new reference duckweed protein database
described by Tao (Tao et al. 2017). The expression level of key enzymes that are responsible for
flavonoid biosynthesis, such as phenylalanine
ammonia-lyase (PAL), cinnamate 4-hydroxylase
(C4H), 4-hydroxycinnamoyl-CoA ligase (4CL),
chalcone synthase (CHS), chalcone isomerase
(CHI), flavanone 3-hydroxylase (F3H), and
anthocyanidin synthase (ANS), was improved,
and the anthocyanin biosynthesis branch-related
enzymes such as F3H, dihydroflavonol
4-reductase (DFR) and ANS expression were
also increased under nutrient starvation in L.
punctata 0202 based on the result of re-analysis
for iTRAQ data, but PAL, C4H, and 4CL were
suppressed immediately by uniconazole treatment. However, almost all the key enzymes of
lignin biosynthetic branch in phenylalanine
metabolic network and 25 laccases assembled by
de novo RNA-Seq were not detected by
re-analysis for iTRAQ data in duckweed under
nutrient starvation and uniconazole treatment.
This study supported previous omics research
that the nutrient starvation treatment could
improve the starch and flavonoid content simultaneously (Tao et al. 2013; Huang et al. 2014)
and suggested that uniconazole treatment could
induce starch accumulation and suppress the
flavonoid content in duckweed (Tao et al. 2017).
14.4 Conclusion
Proteins are the direct undertakers of gene
function. The high-throughput proteomic method
facilitated our understanding of high starch
accumulation mechanism by duckweed at proteome level. Also, it showed powerful in studying mechanism elucidation. However, few
attention was paid to proteome analysis of
duckweed. We encourage more researchers to
focus on this field and thus promote our deepened understanding and wide application of
duckweed.
References
Angel TE, Aryal UK, Hengel SM et al (2012) Mass
spectrometry-based proteomics: existing capabilities
and future directions. Chem Soc Rev 41(10):3912–
3928. https://doi.org/10.1039/c2cs15331a
Chen L, Yu C, Ma Y et al (2016) Insights into the
structural and physicochemical properties of small
granular starches from two hydrophyte duckweeds,
Spirodela oligorrhiza and Lemna minor. Carbohydr
Res 435:208–214. https://doi.org/10.1016/j.carres.
2016.10.010
140
Y. Fang et al.