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Summary: The greater duckweed (Spirodela polyrhiza 7498) exhibits trophic diversity (photoautotrophic, heterotrophic, photoheterotrophic, and mixotrophic growth) depending on the availability of exogenous organic carbon sources and light.Here, we show that the ability to transition between various trophic growth conditions is an advantageous trait, providing great phenotypic plasticity and metabolic flexibility in S. polyrhiza 7498.By comparing S. polyrhiza 7498 growth characteristics, metabolic acclimation, and cellular ultrastructure across these trophic modes, we show that mixotrophy decreases photosynthetic performance and relieves the CO2 limitation of photosynthesis by enhancing the CO2 supply through the active respiration pathway. Proteomic and metabolomic analyses corroborated that S. polyrhiza 7498 increases its intracellular CO2 and decreases reactive oxygen species under mixotrophic and heterotrophic conditions, which substantially suppressed the wasteful photorespiration and oxidative‐damage pathways. As a consequence, mixotrophy resulted in a higher biomass yield than the sum of photoautotrophy and heterotrophy.Our work provides a basis for using trophic transitions in S. polyrhiza 7498 for the enhanced accumulation of value‐added products. [ABSTRACT FROM AUTHOR]

Duckweeds is the most promising nonfood feedstock for sustainable bioenergy production. Mixotrophy is the best growth mode compared to photoautotrophy and heterotrophy for biomass and starch accumulation in duckweed. This work investigated the impacts of light intensities (3,000, 6,000, 9,000, 12,000, 15,000, and 20,000 lux) and exogenous glucose concentrations (5, 10, 15, 20, 30, and 40 g L−1) on the biomass and starch accumulation of mixotrophic duckweed. The results showed that increasing light intensity and the initially applied concentration of glucose enhanced both growth and starch content. However, high concentrations of glucose (15–40 g L−1) resulted in a higher biomass yield but concurrently greatly inhibited photosynthesis. Moreover, excess carbon was redirected into starch biosynthesis under high glucose. The maximum starch yield of 655.4 g m−2 was obtained at 40 g L−1 glucose, with a maximum starch content of 72.7% of dry biomass and a biomass yield of 1024.6 g m−2. The optimum light intensity for starch accumulation was 20,000 lux, with a maximum starch yield of 236.2 g m−2. These results indicated that high organic carbon levels are a robust way to promote starch production in mixotrophic duckweed. • High glucose levels and light intensities boosted biomass and starch production. • Higher glucose levels provided a higher biomass while inhibiting photosynthesis. • More carbon was allocated to starch biosynthesis with higher glucose levels. • 20,000 lux was the optimum light condition for duckweed starch accumulation. • The maximum starch yield of 95.7 t/ha/year was generated at 40 g/L of glucose. [ABSTRACT FROM AUTHOR]

Duckweeds contain high levels of starch and are environmentally sustainable and economically viable feedstock for biofuel production. Here, the biomass and starch yield of three duckweed species under three different nutrient-limited conditions were analyzed to investigate the possible ways of further increasing the efficiency of starch production. The results showed that sulfur limitation resulted in the highest starch yield, which was 42% and 73% higher than in nitrogen or phosphorus limitation conditions, respectively. The high yield of sulfur-limited duckweed is largely due to the combinations of little effects on biomass and high accumulations of starch. Although nitrogen limitation led to higher starch content (67.4%), it severely reduced biomass production. Besides, this work revealed the mechanism of starch accumulation induced by sulfur limitation in duckweed based on transcriptomic analysis. In summary, sulfur limitation is a practical approach to increase starch yields in duckweed without affecting growth or biomass production. • Sulfur limitation induces starch production without inhibiting growth of duckweed. • Starch content was as high as 56.2% of dry weight under sulfur limitation. • Sulfur limitation results in the highest starch yield in three duckweed species. • SDI1 and bZIP17 were identified for improving starch yield by genetic engineering. • The mechanism of sulfur limitation-induced starch accumulation was elucidated. [ABSTRACT FROM AUTHOR]

• Duckweed growth under mixotrophy, heterotrophy and photoautotrophy was compared. • Duckweed metabolized glucose, fructose, galactose, sucrose and maltose. • Mixotrophy was best for biomass production and pollutant uptake. • Heterotrophy is a feasible method for starch induction. • Mixotrophic-heterotrophic cultivation strategy should enhance starch accumulation. Duckweed is a potential biomass source for alternative energy production. This work reports the effects of trophic modes on growth rates, biomass accumulation, and removal rates of pollutant by duckweed. Glucose, fructose, galactose, sucrose, and maltose all supported heterotrophic and mixotrophic growth of duckweed. The mixotrophic growth rate was 4.98 and 6.22 times higher than those in heterotrophic and photoautotrophic conditions, respectively. Notably, mixotrophy produced more biomass than the simple sum of the biomass accumulation during heterotrophy and photoautotrophy. Mixotrophy was also superior in starch and protein production, as well as in removal rates of nutrients and organic carbon from the growth medium. However, the starch content of duckweed grown heterotrophically was 2.06 times higher than in mixotrophy, suggesting a combination of mixotrophy and heterotrophy as an effective strategy for starch-rich biomass production. This study thus provides a paradigm for future studies supporting duckweed-based biomass production and organic wastewater treatment. [ABSTRACT FROM AUTHOR]

WRKY is one of the largest transcription factor families across higher plant species and is involved in important biological processes and plant responses to various biotic/abiotic stresses. However, only a few investigations on WRKYs have been conducted in aquatic plants. This study first systematically analyzed the gene structure, protein properties, and phylogenetic relationship of 693 WRKY s in nine aquatic and two wetland plants at the genome-wide level. The pattern of WRKY groups in two aquatic ferns provided new evidence for the origin and evolution of WRKY genes. ARE cis -regulatory elements show an unusual high frequency in the promoter region of WRKY genes, indicating the adaptation to the aquatic habitat in aquatic plants. The WRKY gene family experienced a series of gene loss events in aquatic plants, especially group III. Further studies were conducted on the interaction network of SpWRKYs, their target genes, and non-coding RNAs. The expression profile of SpWRKYs under phosphate starvation, cold, and submergence conditions revealed that most SpWRKYs are involved in the response to abiotic stresses. Our investigations lay the foundation for further study on the mechanism of WRKYs responding to abiotic stresses in aquatic plants. • 630 WRKYs in 8 aquatic plants and 2 wetland plants were identified or re-identified. • Environmental stress is the main driver in the evolution of WRKYs in aquatic plants. • Segmental/WGD duplication is the major driver of expansion of WRKY gene family. • Contraction is most common form in aquatic/wetland plants, especially the group III members. • Most SpWRKYs were involved in abiotic stresses (phosphate starvation, cold. submergence) under aquatic environment. [ABSTRACT FROM AUTHOR]