Interpretation of the adsorption process of toxic Cd2+ removal by modified sweet potato residue.

Cadmium (Cd) is a common and toxic non-essential heavy metal that must be effectively treated to reduce its threat to the environment and public health. Adsorption with an adsorbent, such as agricultural waste, is widely used to remove heavy metals from wastewater. Sweet potato, the sixth most abundant food crop worldwide, produces a large amount of waste during postharvest processing that could be used as an economic adsorbent. In this study, the feasibility of using sweet potato residue (SPR) as an adsorbent for Cd2+ adsorption was assessed. To enhance the removal rate, SPR was modified with NaOH, and the effects of the modification and adsorption conditions on the removal of Cd2+ from wastewater were investigated. The results showed that modified sweet potato residue (MSPR) could be adapted to various pH and temperatures of simulated wastewater, implying its potential for multi-faceted application. Under optimized conditions, the removal of Cd2+ by MSPR was up to 98.94% with a maximum adsorption capacity of 19.81 mg g-1. Further investigation showed that the MSPR exhibited rich functional groups, a loose surface, and a mesoporous structure, resulting in advantageous characteristics for the adsorption of Cd2+. In addition, the MSPR adsorbed Cd2+ by complexation, ion exchange, and precipitation during a monolayer chemisorption adsorption process. This work demonstrates a sustainable and environment friendly strategy for Cd2+ removal from wastewater and a simple approach for the preparation of MSPR and also revealed the adsorption mechanism of Cd2+ by MSPR, thus providing a suitable adsorbent and strategy for the removal of other heavy metals.

OsMADS1 Regulates Grain Quality, Gene Expressions, and Regulatory Networks of Starch and Storage Protein Metabolisms in Rice.

OsMADS1 plays a vital role in regulating floret development and grain shape, but whether it regulates rice grain quality still remains largely unknown. Therefore, we used comprehensive molecular genetics, plant biotechnology, and functional omics approaches, including phenotyping, mapping-by-sequencing, target gene seed-specific RNAi, transgenic experiments, and transcriptomic profiling to answer this biological and molecular question. Here, we report the characterization of the 'Oat-like rice' mutant, with poor grain quality, including chalky endosperms, abnormal morphology and loose arrangement of starch granules, and lower starch content but higher protein content in grains. The poor grain quality of Oat-like rice was found to be caused by the mutated OsMADS1Olr allele through mapping-by-sequencing analysis and transgenic experiments. OsMADS1 protein is highly expressed in florets and developing seeds. Both OsMADS1-eGFP and OsMADS1Olr-eGFP fusion proteins are localized in the nucleus. Moreover, seed-specific RNAi of OsMADS1 also caused decreased grain quality in transgenic lines, such as the Oat-like rice. Further transcriptomic profiling between Oat-like rice and Nipponbare grains revealed that OsMADS1 regulates gene expressions and regulatory networks of starch and storage protein metabolisms in rice grains, hereafter regulating rice quality. In conclusion, our results not only reveal the crucial role and preliminary mechanism of OsMADS1 in regulating rice grain quality but also highlight the application potentials of OsMADS1 and the target gene seed-specific RNAi system in improving rice grain quality by molecular breeding.

Improving the quality of barren rocky soil by culturing sweetpotato, with special reference to plant-microbes-soil interactions.

Biological process is an effective strategy to improve soil quality in agroecosystems. Sweetpotato has long been cultivated in barren rocky soil (BRS) to improve soil fertility and obtain considerably high yield. However, how sweetpotato cultivation affects soil quality is still unclear. We cultured sweetpotato in virgin BRS, and investigated its transcriptome, rhizospheric microbial community and soil properties. A high sweetpotato yield (22.69 t.ha-1) was obtained through upregulating the expression of genes associated with stress resistance, nitrogen/phosphorus/potassium (N/P/K) uptake, and root exudates transport. Meanwhile, the rhizospheric microbial diversity in BRS increased, and the rhizospheric microbial community structure became more similar to that of fertile soil, which might benefit from the increased root exudates. Notably, the relative abundances of N-fixing and P/K-solubilizing microbes increased, and the copy number of nifH increased 6.67 times. Moreover, the activities of acid, neutral, and alkaline phosphatases increased strongly from 0.63, 0.02, and 1.15-1.58, 0.31, and 2.11 mg phenol·g-1·d-1, respectively, and total carbon, dissolved organic carbon, available N/P content also increased, while bulk density and pH of BRS decreased, indicating the enhanced soil fertility. Our study found sweetpotato cultivation improved BRS quality through shaping microbial communities, which has important guiding significance for sustainable agriculture.

Cell Wall Matrix Polysaccharides Contribute to Salt-Alkali Tolerance in Rice.

Salt-alkali stress threatens the resilience to variable environments and thus the grain yield of rice. However, how rice responds to salt-alkali stress at the molecular level is poorly understood. Here, we report isolation of a novel salt-alkali-tolerant rice (SATR) by screening more than 700 germplasm accessions. Using 93-11, a widely grown cultivar, as a control, we characterized SATR in response to strong salt-alkali stress (SSAS). SATR exhibited SSAS tolerance higher than 93-11, as indicated by a higher survival rate, associated with higher peroxidase activity and total soluble sugar content but lower malonaldehyde accumulation. A transcriptome study showed that cell wall biogenesis-related pathways were most significantly enriched in SATR relative to 93-11 upon SSAS. Furthermore, higher induction of gene expression in the cell wall matrix polysaccharide biosynthesis pathway, coupled with higher accumulations of hemicellulose and pectin as well as measurable physio-biochemical adaptive responses, may explain the strong SSAS tolerance in SATR. We mapped SSAS tolerance to five genomic regions in which 35 genes were candidates potentially governing SSAS tolerance. The 1,4-ß-D-xylan synthase gene OsCSLD4 in hemicellulose biosynthesis pathway was investigated in details. The OsCSLD4 function-disrupted mutant displayed reduced SSAS tolerance, biomass and grain yield, whereas the OsCSLD4 overexpression lines exhibited increased SSAS tolerance. Collectively, this study not only reveals the potential role of cell wall matrix polysaccharides in mediating SSAS tolerance, but also highlights applicable value of OsCSLD4 and the large-scale screening system in developing SSAS-tolerant rice.

Effects of various spectral compositions on micro-polluted water purification and biofuel feedstock production using duckweed.

The purification of micro-polluted water for drinking water can play an important role in solving water crisis. To investigate the effects of spectral composition on nutrient removal and biofuel feedstock production using duckweed, Landoltia punctata was cultivated in different spectral compositions in micro-polluted water. Results showed that the nitrogen and phosphorus removal efficiency were 99.4% and 93.5% at an recommended red and blue light photon intensity mixture ratio of 2:1. Meanwhile, maximum growth rate of duckweed (11.37 g/m2/day) was observed at red/blue = 2:1. In addition, maximum starch accumulation rate of duckweed was found to be 6.12 g/m2/day, with starch content of 36.63% at red/blue = 4:1, which was three times higher when compared to that of white light. Moreover, the recommended ratio of red and blue light was validated by economic efficiency analysis of energy consumptions. These findings provide a sustainable environmental restoration method to transform water micro-pollutants to available substances.

Ammonium detoxification mechanism of ammonium-tolerant duckweed (Landoltia punctata) revealed by carbon and nitrogen metabolism under ammonium stress.

In this work, the ammonium-tolerant duckweed Landoltia punctata 0202 was used to study the effect of ammonium stress on carbon and nitrogen metabolism and elucidate the detoxification mechanism. The growth status, protein and starch content, and activity of nitrogen assimilation enzymes were determined, and the transcriptional levels of genes involved in ion transport and carbon and nitrogen metabolism were investigated. Under high ammonium stress, the duckweed growth was inhibited, especially when ammonium was the sole nitrogen source. Ammonium might mainly enter cells via low-affinity transporters. The stimulation of potassium transport genes suggested sufficient potassium acquisition, precluding cation deficiency. In addition, the up-regulation of ammonium assimilation and transamination indicated that excess ammonium could be incorporated into organic nitrogen. Furthermore, the starch content increased from 3.97% to 16.43% and 26.02% in the mixed-nitrogen and ammonium-nitrogen groups, respectively. And the up-regulated starch synthesis, degradation, and glycolysis processes indicated that the accumulated starch could provide sufficient carbon skeletons for excess ammonium assimilation. The findings of this study illustrated that the coordination of carbon and nitrogen metabolism played a vital role in the ammonium detoxification mechanism of duckweeds.

Low Nitrogen Fertilization Alter Rhizosphere Microorganism Community and Improve Sweetpotato Yield in a Nitrogen-Deficient Rocky Soil.

Sweetpotato can be cultivated in the reclaimed rocky soil in Sichuan Basin, China, which benefits from the release of mineral nutrients in the rocky soil by microorganisms. Shortage of nitrogen (N) in the rocky soil limits sweetpotato yield, which can be compensated through N fertilization. Whereas high N fertilization inhibits biological N fixation and induces unintended environmental consequences. However, the effect of low N fertilization on microorganism community and sweetpotato yield in the N-deficient rocky soil is still unclear. We added a low level of 1.5 g urea/m2 to a rocky soil cultivated with sweetpotato, and measured rocky soil physiological and biochemical properties, rhizosphere microbial diversity, sweetpotato physiological properties and transcriptome. When cultivating sweetpotato in the rocky soil, low N fertilization (1.5 g urea/m2) not only improved total N (TN) and available N (AN) in the rocky soil, but also increased available phosphorus (AP), available potassium (AK), and nitrogenase and urease activity. Interestingly, although low N fertilization could reduce bacterial diversity through affecting sweetpotato root exudates and rocky soil properties, the relative abundance of P and K-solubilizing bacteria, N-fixing and urease-producing bacteria increased under low N fertilization, and the relative abundance of plant pathogens decreased. Furthermore, low N fertilization increased the phytohormones, such as zeatin riboside, abscisic acid, and methyl jasmonate contents in sweetpotato root. Those increases were consistent with our transcriptome findings: the inhibition of the lignin synthesis, the promotion of the starch synthesis, and the upregulated expression of Expansin, thus resulting in promoting the formation of tuberous roots and further increasing the sweetpotato yield by half, up to 3.3 kg/m2. This study indicated that low N fertilization in the N-deficient rocky soil improved this soil quality through affecting microorganism community, and further increased sweetpotato yield under regulation of phytohormones pathway.

Unraveling the Contribution of High Temperature Stage to Jiang-Flavor Daqu, a Liquor Starter for Production of Chinese Jiang-Flavor Baijiu, With Special Reference to Metatranscriptomics.

Jiang-flavor (JF) daqu is a liquor starter used for production of JF baijiu, a well-known distilled liquor in China. Although a high temperature stage (70°C) is necessary for qualifying JF daqu, little is known regarding its active microbial community and functional enzymes, along with its role in generating flavor precursors for JF baijiu aroma. In this investigation, based on metatranscriptomics, fungi, such as Aspergillus and Penicillium, were identified as the most active microbial members and 230 carbohydrate-active enzymes were identified as potential saccharifying enzymes at 70°C of JF daqu. Notably, most of enzymes in identified carbohydrate and energy pathways showed lower expression levels at 70°C of JF daqu than those at the high temperature stage (62°C) of Nong-flavor (NF) daqu, indicating lowering capacities of saccharification and fermentation by high temperature stage. Moreover, many enzymes, especially those related to the degradation of aromatic compounds, were only detected with low expression levels at 70°C of JF daqu albeit not at 62°C of NF daqu, indicating enhancing capacities of generating special trace aroma compounds in JF daqu by high temperature stage. Additionally, most of enzymes related to those capacities were highly expressed at 70°C by fungal genus of Aspergillus, Coccidioides, Paracoccidioides, Penicillium, and Rasamsonia. Therefore, this study not only sheds light on the crucial functions of high temperature stage but also paves the way to improve the quality of JF baijiu and provide active community and functional enzymes for other fermentation industries.

OsSPL18 controls grain weight and grain number in rice.

Grain weight and grain number are two important traits directly determining grain yield in rice. To date, a lot of genes related to grain weight and grain number have been identified; however, the regulatory mechanism underlying these genes remains largely unknown. In this study, we studied the biological function of OsSPL18 during grain and panicle development in rice. Knockout (KO) mutants of OsSPL18 exhibited reduced grain width and thickness, panicle length and grain number, but increased tiller number. Cytological analysis showed that OsSPL18 regulates the development of spikelet hulls by affecting cell proliferation. qRT-PCR and GUS staining analyses showed that OsSPL18 was highly expressed in developing young panicles and young spikelet hulls, in agreement with its function in regulating grain and panicle development. Transcriptional activation experiments indicated that OsSPL18 is a functional transcription factor with activation domains in both the N-terminus and C-terminus, and both activation domains are indispensable for its biological functions. Quantitative expression analysis showed that DEP1, a major grain number regulator, was significantly down-regulated in OsSPL18 KO lines. Both yeast one-hybrid and dual-luciferase (LUC) assays showed that OsSPL18 could bind to the DEP1 promoter, suggesting that OsSPL18 regulates panicle development by positively regulating the expression of DEP1. Sequence analysis showed that OsSPL18 contains the OsmiR156k complementary sequence in the third exon; 5' RLM-RACE experiments indicated that OsSPL18 could be cleaved by OsmiR156k. Taken together, our results uncovered a new OsmiR156k-OsSPL18-DEP1 pathway regulating grain number in rice.

Frond transformation system mediated by Agrobacterium tumefaciens for Lemna minor.

The Lemnaceae, known as duckweed, the smallest flowering aquatic plant, shows promise as a plant bioreactor. For applying this potential plant bioreactor, establishing a stable and efficient genetic transformation system is necessary. The currently favored callus-based method for duckweed transformation is time consuming and genotype limited, as it requires callus culture and regeneration, which is inapplicable to many elite duckweed strains suitable for bioreactor exploitation. In this study, we attempted to establish a simple frond transformation system mediated by Agrobacterium tumefaciens for Lemna minor, one of the most widespread duckweed species in the world. To evaluate the feasibility of the new transformation system, the gene CYP710A11 was overexpressed to improve the yield of stigmasterol, which has multiple medicinal purposes. Three L. minor strains, ZH0055, D0158 and M0165, were transformed by both a conventional callus transformation system (CTS) and the simple frond transformation system (FTS). GUS staining, PCR, quantitative PCR and stigmasterol content detection showed that FTS can produce stable transgenic lines as well as CTS. Moreover, compared to CTS, FTS can avoid the genotype constraints of callus induction, thus saving at least half of the required processing time (CTS took 8-9 months while FTS took approximately 3 months in this study). Therefore, this transformation system is feasible in producing stable transgenic lines for a wide range of L. minor genotypes.

The DTH8-Hd1 Module Mediates Day-Length-Dependent Regulation of Rice Flowering.

Photoperiodic flowering is one of the most important pathways to govern flowering in rice (Oryza sativa), in which Heading date 1 (Hd1), an ortholog of the Arabidopsis CONSTANS gene, encodes a pivotal regulator. Hd1 promotes flowering under short-day conditions (SD) but represses flowering under long-day conditions (LD) by regulating the expression of Heading date 3a (Hd3a), the FLOWERING LOCUS T (FT) ortholog in rice. However, the molecular mechanism of how Hd1 changes its regulatory activity in response to day length remains largely unknown. In this study, we demonstrated that the repression of flowering in LD by Hd1 is dependent on the transcription factor DAYS TO HEADING 8 (DTH8). Loss of DTH8 function results in the activation of Hd3a by Hd1, leading to early flowering. We found that Hd1 directly interacts with DTH8 and that the formation of the DTH8-Hd1 complex is necessary for the transcriptional repression of Hd3a by Hd1 in LD, implicating that the switch of Hd1 function is mediated by DTH8 in LD rather than in SD. Furthermore, we revealed that DTH8 associates with the Hd3a promoter to modulate the level of H3K27 trimethylation (H3K27me3) at the Hd3a locus. In the presence of the DTH8-Hd1 complex, the H3K27me3 level was increased at Hd3a, whereas loss of DTH8 function resulted in decreased H3K27me3 level at Hd3a. Taken together, our findings indicate that, in response to day length, DTH8 plays a critical role in mediating the transcriptional regulation of Hd3a by Hd1 through the DTH8-Hd1 module to shape epigenetic modifications in photoperiodic flowering.

OsELF3-1, an ortholog of Arabidopsis early flowering 3, regulates rice circadian rhythm and photoperiodic flowering.

Arabidopsis thaliana early flowering 3 (ELF3) as a zeitnehmer (time taker) is responsible for generation of circadian rhythm and regulation of photoperiodic flowering. There are two orthologs (OsELF3-1 and OsELF3-2) of ELF3 in rice (Oryza sativa), but their roles have not yet been fully identified. Here, we performed a functional characterization of OsELF3-1 and revealed it plays a more predominant role than OsELF3-2 in rice heading. Our results suggest OsELF3-1 can affect rice circadian systems via positive regulation of OsLHY expression and negative regulation of OsPRR1, OsPRR37, OsPRR73 and OsPRR95 expression. In addition, OsELF3-1 is involved in blue light signaling by activating early heading date 1 (Ehd1) expression to promote rice flowering under short-day (SD) conditions. Moreover, OsELF3-1 suppresses a flowering repressor grain number, plant height and heading date 7 (Ghd7) to indirectly accelerate flowering under long-day (LD) conditions. Taken together, our results indicate OsELF3-1 is essential for circadian regulation and photoperiodic flowering in rice.