Corrigendum: Expression of Pumpkin CmbHLH87 Gene Improves Powdery Mildew Resistance in Tobacco.

[This corrects the article DOI: 10.3389/fpls.2020.00163.].

Expression of Pumpkin CmbHLH87 Gene Improves Powdery Mildew Resistance in Tobacco.

Powdery mildew (PM), caused by Podosphaera xanthii, is a major threat to the global cucurbit yield. The molecular mechanisms underlying the PM resistance of pumpkin (Cucurbita moschata Duch.) are largely unknown. A homolog of the basic helix-loop-helix (bHLH) transcription factor was previously identified through a transcriptomic analysis of a PM-resistant pumpkin. In this study, this bHLH homolog in pumpkin has been functionally characterized. CmbHLH87 is present in the nucleus. CmbHLH87 expression in the PM-resistant material was considerably downregulated by PM; and abscisic acid, methyl jasmonate, ethephon, and NaCl treatments induced CmbHLH87 expression. Ectopic expression of CmbHLH87 in tobacco plants alleviated the PM symptoms on the leaves, accelerated cell necrosis, and enhanced H2O2 accumulation. The expression levels of PR1a, PR5, and NPR1 were higher in the PM-infected transgenic plants than in PM-infected wild-type plants. Additionally, the chlorosis and yellowing of plant materials were less extensive and the concentration of bacteria at infection sites was lower in the transgenic tobacco plants than in the wild-type plants in response to bacterial wilt and scab pathogens. CmbHLH87 may be useful for genetic engineering of novel pumpkin cultivars in the future.

[Occurrence of Denitrifying Dephosphatation in a Hybrid Constructed Wetland System and Its Stability].

This study was conducted to explore the startup characteristics and stability of a hybrid constructed wetland (HCW) system with a denitrifying dephosphatation process, which was composed of two tidal flow-constructed wetlands (termed T-A and T-B). As the system was operated according to the two-time feeding tidal flow operation mode, denitrifying dephosphatation and nitrification could be respectively enhanced in T-A and T-B, and the HCW achieved ideal simultaneous denitrification and phosphorus removal effects when treating domestic sewage. The introduction of periodical carbon source supplements for phosphorus harvesting alleviated excessive phosphorus accumulation in T-A and increased the storage of PHB within denitrifying phosphate-accumulating organisms (DPAOs). Subsequently, a stable and efficient denitrifying phosphorus removal effect could be guaranteed to some extent as the HCW system was operated during the test. As the phosphorus harvesting cycle length was 30 d, the mean phosphorus recovery efficiency of the HCW system was 63.97% throughout the experiment. Regarding the typical cycle, the mean TP and NOx--N removal efficiencies of T-A could respectively achieve (97.86±0.70)% and (98.29±2.62)% during the denitrifying dephosphatation process, and the amounts of phosphorus release and PHB synthesis in T-A could also reach up to (1486.29±123.25) mg and (4.43±0.57) mmol·g-1, respectively, during the phosphorus harvesting process. Meanwhile, the utilization rate of the supplementary carbon in the system was (94.65±2.66)%. To summarize, this study offers a new method for simultaneous denitrification and phosphorus removal in constructed wetlands, and expands the development and application range of phosphorus recovery processes.

[Mechanism of Pre-ozonation Enhanced Coagulation on DON in the Secondary Effluent].

Municipal wastewater effluent is increasingly used as reclaimed water and source water for downstream areas. Scholars are beginning to study the potential of dissolved organic nitrogen (DON) as a precursor to the formation of nitrogen disinfection by-products (DBP). In order to explore the mechanism of pre-ozonation coupled with enhanced coagulation on DON in the secondary effluent, the distributions of molecular weight and hydrophobicity/hydrophilicity of DON were analyzed. Disinfection by-product formation potential from chlorination was also investigated. Lastly, the composition and chemical structure of DON before and after coagulation were studied in combination with 3DEEM. Our results showed that pre-ozonation followed by coagulation with PACl significantly enhanced the removal of DON and mitigated DBP formation potentials. The following conclusions can be drawn from this study:① The tested effluent was very hard as indicated by total hardness and high calcium concentrations, and the pH had an important effect on pre-ozonation enhanced coagulation. As pH was decreased, the rates of DON, DOC and UV254 removal increased. At pH 6.2, the rate of DON removal was maximal, and a 3.7 fold increase in removal-rate was achieved. ② Calcium played a critical role in pre-ozonation enhanced coagulation. Zeta potentials and calcium concentrations were substantially affected at higher ozone doses. At ozone dosage of 8 mg·L-1, Zeta potentials increased from -33 to -8 mV, and calcium concentrations decreased from 116 to 89 mg·L-1. The ratio of calcium hardness to DOC was relatively high in this study, approaching 24 mg·mg-1 (CaCO3/DOC). Thus, pre-ozonation promoted the removal of DON by coagulation. ③ Large molecular weight and hydrophobic DON were easier to remove by coagulation. Ozonation modified the DON characteristics to become more hydrophilic and smaller in molecular weight. Coagulation reduced overall DBP formation potentials to less than 20%. Pre-ozonation enhanced coagulation decreased overall DBP formation potentials by more than 45%. ④ Finally, the 3DEEM spectra indicated that the formation potentials and DON characteristics, due to disinfection, were related to three main peaks, which corresponded to tryptophan-based proteins, aromatic proteins, and fulvic acids.

Ectopic Expression of the Chinese Cabbage Malate Dehydrogenase Gene Promotes Growth and Aluminum Resistance in Arabidopsis.

Malate dehydrogenases (MDHs) are key metabolic enzymes that play important roles in plant growth and development. In the present study, we isolated the full-length and coding sequences of BraMDH from Chinese cabbage [Brassica campestris L. ssp. pekinensis (Lour) Olsson]. We conducted bioinformatics analysis and a subcellular localization assay, which revealed that the BraMDH gene sequence contained no introns and that BraMDH is localized to the chloroplast. In addition, the expression pattern of BraMDH in Chinese cabbage was investigated, which revealed that BraMDH was heavily expressed in inflorescence apical meristems, as well as the effect of BraMDH overexpression in two homozygous transgenic Arabidopsis lines, which resulted in early bolting and taller inflorescence stems. Furthermore, the fresh and dry weights of aerial tissue from the transgenic Arabidopsis plants were significantly higher than those from the corresponding wild-type plants, as were plant height, the number of rosette leaves, and the number of siliques produced, and the transgenic plants also exhibited stronger aluminum resistance when treated with AlCl3. Therefore, our results suggest that BraMDH has a dramatic effect on plant growth and that the gene is involved in both plant growth and aluminum resistance.

[Chlorination characteristic and disinfection by-product formation potential of dissolved organic nitrogen compounds in municipal wastewater].

In order to explore the chlorinated disinfection by-product formation potential and chemical structure of dissolved organic nitrogen compounds in municipal wastewater, the water quality parameters, such as DON, DOC, NH4(+) -N and UV254 etc, were determined in the secondary effluent and the molecular weight distribution of the DON was investigated before and after the reaction with chlorine. DBPs were determined by gas chromatography, and the changes of DON were characterized using Fourier transform infrared spectroscopy and three-dimensional fluorescence spectroscopy before and after the reaction with chlorine. The results showed that DON, DOC, NH4(+) -N and UV254 were 2.47 mg x L(-1), 14.45 mg x L(-1), 5.42 mg x L(-1) and 15.88 m(-1), and m(DOC)/m(DON) and SUVA were 5.85 mg x mg(-1) and 1.09 L x (m x mg)(-1) in the secondary effluent. After the reaction with chlorine, the proportion of small molecular weight (M(r) < 6 000) DON increased from 78% to 70% , and the proportion of large molecular weight (M(r) > 20 000) DON decreased from 21% to 14%. The medium molecular weight (M(r)6000-20000) DON accounted for a small proportion and was unchanged. Among the DBPs, the concentration of bromochloroacetonitrile was the highest, which was 6.887 microg x L(-1), and the concentration of trichloroacetonitrile was the lowest, which was only 0.217 microg x L(-1). In FTIR spectrum, the dominating bands were at 3 500-3 400, 2 260-2 200, 1 700-1 640, 1 500-1 450, 1 150-1 100 and 850-800 cm(-1) respectively before the reaction, and the 1 380-1 350 cm(-1) and 600-550 cm(-1) bands were the dominating bands in addition to the original absorbing regions after the reaction. 3DEEM revealed that the variation of DON depends intimately on tryptophan protein-like substances, aromatic protein-like substances and fulvic acid-like substances.

[Removal of DON in micro-polluted raw water by coagulation and adsorption using activated carbon].

Dissolved organic nitrogen as a precursor of new type nitrogenous disinfection by-products in drinking water attracted gradually the attention of scholars all over the world. In order to explore the mechanism of DON removal in micro-polluted raw water by coagulation and adsorption, water quality parameters, such as DON, DOC, NH4(+) -N, UV254, pH and dissolved oxygen, were determined in raw water and the molecular weight distribution of the DON and DOC was investigated. The variations in DON, DOC and UV254 in the coagulation and adsorption tests were investigated, and the changes of DON in raw water were characterized using three-dimensional fluorescence spectroscopy. The results showed that DON, DOC and UV254 were 1.28 mg x L(-1), 8.56 mg x L(-1), 0.16 cm(-1), and DOC/DON and SUVA were 6.69 mg x mg(-1), 1.87 m(-1) x (mg x L(-1))(-1) in raw water, respectively. The molecular weight distribution of the DON in raw water showed a bimodal distribution. The small molecular weight (< 6 000) fractions accounted for a high proportion of 68% and the large (> 20 000) fractions accounted for about 22%. The removal of DON, DOC and UV254 was about 20%, 26% and 70%, respectively, in the coagulation test and the dosage of coagulant was 10 mg x L(-1). The removal of DON, DOC and UV254 was about 60%, 35% and 100%, respectively, in the adsorption test and the dosage of activated carbon was 1.0 g. In the combination of coagulation and adsorption, the removal of DON and DOC reached approximately 82% and 64%, respectively. 3DEEM revealed that the variation of DON in the coagulation and adsorption tests depended intimately on tryptophan protein-like substances, aromatic protein-like substances and fulvic acid-like substances.

A vacuolar processing enzyme RsVPE1 gene of radish is involved in floral bud abortion under heat stress.

Radish floral bud abortion (FBA) is an adverse biological phenomenon that occurs during reproduction. Although FBA is a frequent occurrence, its molecular mechanism remains unknown. A transcript-derived fragment (TDF72), which was obtained by cDNA amplified fragment length polymorphism (cDNA-AFLP), was up-regulated in the aborted buds and exhibited 89% sequence homology with the AtγVPE gene. In this study, TDF72 was used to clarify the role of VPE in FBA by isolation of the VPE gene RsVPE1 from radish flower buds. The full-length genomic DNA was 2346 bp including nine exons and eight introns. The full-length cDNA was 1825 bp, containing a complete open reading frame (ORF) of 1470 bp, which encoded a predicted protein containing 489 amino acid residues, with a calculated molecular mass of 53.735 kDa. Expression analysis demonstrated that RsVPE1 was expressed in all tested organs of radish at different levels. Highest expression was detected in aborted flower buds, suggesting that RsVPE1 has a role in FBA. In order to analyze the role of RsVPE1 in FBA, RsVPE1 was overexpressed in transgenic Arabidopsis thaliana plants. Aborted flower buds appeared in transgenic plants subjected to heat stress. In addition, RsVPE1 expression in the transgenic plants reached a maximum when subjected to heat stress for 24 h and increased by 2.1-fold to 2.8-fold in three homozygous transgenic lines. These results indicated that RsVPE1 led to FBA when its expression levels exceeded a particular threshold, and provided evidence for the involvement of RsVPE1 in promoting FBA under heat stress.

[Mechanism of NH(4+)-N removal in drinking water biofilter].

In order to explore the mechanism of NH(4+)-N removal in drinking water biofilter, water quality parameters, such as NH(4+)-N, NO(2-)-N, NO(3-)-N, total phosphorus, permanganate index, nitrogen gas, temperature and dissolved oxygen etc, were determined in the inflow and outflow of biofilter. Samples of granular activated carbon (GAC) at different height (0, 10, 20, 40, 60 cm) of the biofiter media were collected and analyzed for the bacterial community with molecular biology techniques. The bacterial diversity in the activated carbon biofilm sample was studied based on the phylogenetic analysis of sequences. The results showed that there were three stages according to the NH(4+)-N concentration in the influent. The "nitrogen loss" phenomenon (total inorganic nitrogen in the effluent was less than that in the influent) occurred at the first, second and third stages and the amount of nitrogen loss were 0.94, 0.32 and 0.15 mg x L(-1), respectively. The amount of nitrogen loss had a good positive correlation with the NH(4+)-N concentration in the influent, but not a linear relationship with the concentration of the permanganate index in the influent. The average concentrations of N2 increased gradually with the height of media in the biofilter, with values of 14.04 and 14.67 mg x L(-1) in the influent and the effluent, respectively. Based on the sequencing results, the ammonia-oxidizing bacteria (AOB) in the activated carbon biofilm were classified into three common genera: Nitrosococcus, Nitrosomonas and Nitrosospira. When the NH(4+)-N concentration in the influent was relatively high, the "nitrogen loss" phenomenon in biofilter was caused by the AOB.

[Effects of cadmium and lead on subcellular distribution and chemical form of zinc in Potentilla griffithii var. velutina].

Using the differential centrifugation technique and sequential chemical extraction method, effects of Cd, Pb and different Zn salts on subcellular distribution and chemical form of Zn in Zn hyperaccumulator Potentilla griffithii var. velutina under nutrient solution culture were analyzed. Under all treatments except for the control, 46%-74% and 16%-33% of total Zn in the plants are distributed in cell wall and in soluble fraction, respectively. Further, 74%-95% of total Zn are localized in these two parts under all treatments, which suggest that cell wall and soluble fraction in the plant are major storage sites for Zn. Compared with the control, Zn percentage significantly increases by 9%-38% in the cell wall and decreases by 6%-40% in the soluble fraction with addition of Zn, Cd and Pb treatment (p < 0.05). Although the addition of Cd and Pb has no influence on the pattern of Zn subcellular distribution presenting cell wall > soluble fraction > karyon and chloroplast > mitochondrion, it generally reduces Zn percentage in the chloroplast, karyon and mitochondrion and increases that in the cell wall or soluble fraction, suggesting that Cd and Pb promote the transferring processes of Zn from organelle to either cell wall or vacuole. As to the chemical forms, 61%-87% of total Zn exist as ethanol- and water-extractable forms in plants under control and only leaves under Zn addition treatment; while 62%-73% of total Zn exist as NaCl- and ethanol-extractable forms in leafstalks and roots under Zn addition treatment. NaCl-, ethanol- and water-extractable forms are also the main chemical forms in the plants, occupied almost 70%-89% of total Zn under Zn/Cd and Zn/Pb compound treatments. The addition of Zn, Cd and Pb generally increases the percentage of NaCl-extractable Zn forms, but decreases that of ethanol-extractable Zn, which facilitates Zn chemical form transferring from relatively higher active forms to less active ones. These results mentioned above indicate that cell wall binding, vacuolar compartmentalization and reduction of total percentage in higher active chemical forms are main tolerance mechanisms for Zn in Potentilla griffithii var. velutina in response to Zn, Zn/Cd and Zn/Pb treatments. Additionally, different Zinc salts have no obvious influence on Zn subcellular distribution in the plant, whereas the treatment of Zinc nitrate turns Zn ethanol-extraction to a dominant chemical form.