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.