Comparative transcriptome analysis to investigate the high starch accumulation of duckweed (Landoltia punctata) under nutrient starvation

Abstract

BackgroundDuckweed 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.ResultsThis 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.ConclusionOur 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.

Potential of duckweed in the conversion of wastewater nutrients to valuable biomass: A pilot-scale comparison with water hyacinth

“…By contrast, previous studies have indicated that duckweed showed huge potential in high-starch accumulation during nutrient starvation (Tao et al, 2013;Xiao et al, 2013). The results of the high-starch accumulation experiment showed that the duckweed dry biomass per square meter increased from 16.31 ± 1.43 g/m 2 to 59.68 ± 0.81 g/m 2 in 11 days, and the average growth rate for 11 days was 3.93 ± 0.90 g DW/m 2 /d, which was lower than that in the wastewater.…”

Effect of nitrogen and phosphorus deficiency on transcriptional regulation of genes encoding key enzymes of starch metabolism in duckweed ( Landoltia punctata )

“…The strains of L. punctata 0202 used in this study were isolated from the ponds of Chengdu, China, as done previously (Tao et al, 2013). Upon collection, the plants were rinsed gently with distilled water to remove debris and then the healthy fronds were placed in plastic aquaria containing Hoagland solution comprised of macronutrients (1 mM KH 2 PO 4 , 10 mM KNO 3 , 2 mM Ca(NO 3 ) 2 , and 2 mM MgSO 4 ), micronutrients (46 uM H 3 BO 3 , 9 uM MnCl 2 .4H 2 O, 0.76 uM ZnSO 4 .7H 2 O, 0.32 uM CuSO 4 , and 0.55 uM H 2 MoO 4 ), and an iron source (78 uM Fe-EDTA).…”

“…The PCR reactions were performed utilizing Real-Time PCR System iQ5 (Bio-Rad, USA). We designed the primers for LeAPL2, LeAPL3, LeSSS, LeAMY, and LeBMY according to the transcription sequencing data of our previous experiment (Tao et al, 2013), while the primers of LeAPL1 and LeAPS were designed based on the cDNA of LeAP-L1(Genbank accession number KJ603244) and LeAPS (Genbank accession number KJ603243), respectively (Table 1). We performed qRT-PCR with the gene-specific primer pairs listed in Table 1 using the following parameters: 30 s at 95 C, 40 cycles of 5 s at 95 C, and 30 s at 60 C. PCR products were melted by gradually increasing the temperature from 55 to 95 in 0.5 C increments.…”

“…However, these plants compete with crop plants for an insufficient amount of agricultural land and cause adverse impacts on food security. Therefore, there is an urgent need to develop sustainable feed stock for bioethanol production (Tao et al, 2013).…”

“…Among these, the nutrient content of water has been found to have a direct influence on duckweed growth and starch accumulation. In our previous experiments, the total starch weight of duckweed increased by 42 fold from 1 to 7d when cultured in distilled water (Tao et al, 2013).…”