Abstract
BACKGROUND: Duckweed can thrive on anthropogenic wastewater and produce tremendous biomass production. Due to its relatively high starch and low lignin percentage, duckweed is a good candidate for bioethanol fermentation. Previous studies have observed that water devoid of nutrients is good for starch accumulation, but its molecular mechanism remains unrevealed. RESULTS: This study globally analyzed the response to nutrient starvation in order to investigate the starch accumulation in duckweed (Landoltia punctata). L. punctata was transferred from nutrient-rich solution to distilled water and sampled at different time points. Physiological measurements demonstrated that the activity of ADP-glucose pyrophosphorylase, the key enzyme of starch synthesis, as well as the starch percentage in duckweed, increased continuously under nutrient starvation. Samples collected at 0 h, 2 h and 24 h time points respectively were used for comparative gene expression analysis using RNA-Seq. A comprehensive transcriptome, comprising of 74,797 contigs, was constructed by a de novo assembly of the RNA-Seq reads. Gene expression profiling results showed that the expression of some transcripts encoding key enzymes involved in starch biosynthesis was up-regulated, while the expression of transcripts encoding enzymes involved in starch consumption were down-regulated, the expression of some photosynthesis-related transcripts were down-regulated during the first 24 h, and the expression of some transporter transcripts were up-regulated within the first 2 h. Very interestingly, most transcripts encoding key enzymes involved in flavonoid biosynthesis were highly expressed regardless of starvation, while transcripts encoding laccase, the last rate-limiting enzyme of lignifications, exhibited very low expression abundance in all three samples. CONCLUSION: Our study provides a comprehensive expression profiling of L. punctata under nutrient starvation, which indicates that nutrient starvation down-regulated the global metabolic status, redirects metabolic flux of fixed CO2 into starch synthesis branch resulting in starch accumulation in L. punctata.
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Claims 10
Claim · model-written summary
ADP-glucose pyrophosphorylase activity rose continuously under nutrient starvation.
- Treatment
- nutrient starvatione0
- Gene
- ADP-glucose pyrophosphorylasee0
- Outcome
- activity of ADP-glucose pyrophosphorylasee0
- Direction
- increased continuouslye0
LemnaNot reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the activity of ADP-glucose pyrophosphorylase, the key enzyme of starch synthesis, as well as the starch percentage in duckweed, increased continuously under nutrient starvation”
Claim · model-written summary
Duckweed starch percentage rose continuously under nutrient starvation.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the starch percentage in duckweed, increased continuously under nutrient starvation”
Claim · model-written summary
A de novo duckweed transcriptome contained 74,797 contigs.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A comprehensive transcriptome, comprising of 74,797 contigs, was constructed by a de novo assembly of the RNA-Seq reads”
t0“duckweed”
Claim · model-written summary
Transcripts for starch biosynthesis enzymes were up-regulated.
- Outcome
- expression of some transcripts encoding key enzymes involved in starch biosynthesise0
- Direction
- up-regulatede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the expression of some transcripts encoding key enzymes involved in starch biosynthesis was up-regulated”
t0“duckweed”
Claim · model-written summary
Transcripts for starch consumption enzymes were down-regulated.
- Outcome
- expression of transcripts encoding enzymes involved in starch consumptione0
- Direction
- down-regulatede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the expression of transcripts encoding enzymes involved in starch consumption were down-regulated”
t0“duckweed”
Claim · model-written summary
Some photosynthesis-related transcripts declined during the first 24 h.
- Outcome
- expression of some photosynthesis-related transcriptse0
- Direction
- down-regulatede0
- Qualifier
- during the first 24 he0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the expression of some photosynthesis-related transcripts were down-regulated during the first 24 h”
t0“duckweed”
Claim · model-written summary
Some transporter transcripts rose within the first 2 h.
- Outcome
- expression of some transporter transcriptse0
- Direction
- up-regulatede0
- Qualifier
- within the first 2 he0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the expression of some transporter transcripts were up-regulated within the first 2 h”
t0“duckweed”
Claim · model-written summary
Most flavonoid biosynthesis enzyme transcripts remained highly expressed regardless of starvation.
- Outcome
- transcripts encoding key enzymes involved in flavonoid biosynthesise0
- Direction
- highly expressede0
- Qualifier
- regardless of starvatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“most transcripts encoding key enzymes involved in flavonoid biosynthesis were highly expressed regardless of starvation”
t0“duckweed”
Claim · model-written summary
Laccase transcripts had very low abundance in all three samples.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“transcripts encoding laccase, the last rate-limiting enzyme of lignifications, exhibited very low expression abundance in all three samples”
t0“duckweed”
Claim · model-written summary
The authors infer nutrient starvation redirects fixed CO2 toward starch synthesis.
- Taxon
- L. punctata
Landoltia punctatae0 - Treatment
- nutrient starvatione0
- Outcome
- starch accumulatione0
- Qualifier
- redirects metabolic flux of fixed CO2 into starch synthesis branche0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“nutrient starvation down-regulated the global metabolic status, redirects metabolic flux of fixed CO2 into starch synthesis branch resulting in starch accumulation in L. punctata”