Zinc-finger protein MdBBX7/MdCOL9, a target of MdMIEL1 E3 ligase, confers drought tolerance in apple.

Water deficit is one of the main challenges for apple (Malus × domestica) growth and productivity. Breeding drought-tolerant cultivars depends on a thorough understanding of the drought responses of apple trees. Here, we identified the zinc-finger protein B-BOX 7/CONSTANS-LIKE 9 (MdBBX7/MdCOL9), which plays a positive role in apple drought tolerance. The overexpression of MdBBX7 enhanced drought tolerance, whereas knocking down MdBBX7 expression reduced it. Chromatin immunoprecipitation-sequencing (ChIP-seq) analysis identified one cis-element of MdBBX7, CCTTG, as well as its known binding motif, the T/G box. ChIP-seq and RNA-seq identified 1,197 direct targets of MdBBX7, including ETHYLENE RESPONSE FACTOR (ERF1), EARLY RESPONSIVE TO DEHYDRATION 15 (ERD15), and GOLDEN2-LIKE 1 (GLK1) and these were further verified by ChIP-qPCR and electronic mobility shift assays. Yeast two-hybrid screen identified an interacting protein of MdBBX7, RING-type E3 ligase MYB30-INTERACTING E3 LIGASE 1 (MIEL1). Further examination revealed that MdMIEL1 could mediate the ubiquitination and degradation of MdBBX7 by the 26S proteasome pathway. Genetic interaction analysis suggested that MdMIEL1 acts as an upstream factor of MdBBX7. In addition, MdMIEL1 was a negative regulator of the apple drought stress response. Taken together, our results illustrate the molecular mechanisms by which the MdMIEL1-MdBBX7 module influences the response of apple to drought stress.

Enhanced cadmium immobilization by sulfate-mediated microbial zero-valent iron corrosion.

A biotic iron (Fe0) treatment system combined with mixed microorganisms was applied to remediate cadmium (Cd)-contaminated groundwater under the intervention of sulfate. Due to hydrogenotrophic desulfuration effect, severe iron corrosion was observed in this microbe-collaborative Fe0 system according to surface morphology analysis as lots of secondary minerals (e.g. magnetite, green rust and lepidocrocite) were generated, which was essential for Cd(II) adsorption and immobilization. The sulfate-mediated biotic Fe0 system thereafter achieved a significantly enhanced Cd(II) removal efficiency of 86.1%, over 3.3 times than that in the abiotic Fe0 system. Increasing initial sulfate concentration could improve the removal of cadmium, which further proved that hydrogenotrophic desulfuration played a key role for enhanced Cd removal. According to the experimental results and current reports, the mechanism of Cd(II) removal was revealed into three pathways including adsorption to secondary iron minerals, co-precipitation with iron (hydr)oxides and formation of cadmium sulfide precipitation. Increasing Fe0 dosages showed positive correlation to Cd(II) removal and neutral pH was preferred to sulfate-mediated biotic Fe0 corrosion. These results indicated that sulfate-mediated biotic Fe0 corrosion could greatly relieve the limitation of Fe0 in Cd(II) immobilization, which could be a promising method to eliminate Cd(II) pollution from groundwater.

Insights into the effect of human civilization on Malus evolution and domestication.

The evolutionary history of the Malus genus has not been well studied. In the current study, we presented genetic evidence on the origin of the Malus genus based on genome sequencing of 297 Malus accessions, revealing the genetic relationship between wild species and cultivated apples. Our results demonstrated that North American and East Asian wild species are closer to the outgroup (pear) than Central Asian species, and hybrid species including natural (separated before the Pleistocene, about 2.5 Mya) and artificial hybrids (including ornamental trees and rootstocks) are between East and Central Asian wild species. Introgressions from M. sylvestris in cultivated apples appeared to be more extensive than those from M. sieversii, whose genetic background flowed westward across Eurasia and eastward to wild species including M. prunifolia, M. × asiatica, M. × micromalus, and M. × robust. Our results suggested that the loss of ancestral gene flow from M. sieversii in cultivated apples accompanied the movement of European traders around the world since the Age of Discovery. Natural SNP variations showed that cultivated apples had higher nucleotide diversity than wild species and more unique SNPs than other apple groups. An apple ERECTA-like gene that underwent selection during domestication on 15th chromosome was identified as a likely major determinant of fruit length and diameter, and an NB-ARC domain-containing gene was found to strongly affect anthocyanin accumulation using a genome-wide association approach. Our results provide new insights into the origin and domestication of apples and will be useful in new breeding programmes and efforts to increase fruit crop productivity.

An evaluation of life cycle assessment of European milk production.

Life cycle assessment (LCA) is a method regulated by ISO that conveys the environmental impact of products. LCA studies of the same product should be comparable to benefit environmental policy making. LCA of milk production has evaluated environmental issues such as greenhouse gas emissions, resource utilisation and land use change. Thirteen LCA studies of European milk production were analysed for comparability, and direct comparison was difficult due to technical issues, arbitrary choices and inconsistent assumptions. The strengths and weaknesses of LCA for evaluating an agricultural system are identified and improvements for comparability of future studies are also considered. Future LCA of milk production should ensure that: (1) the production system is appropriately characterized according to the goal of study; (2) a clear description of the system boundary and allocation procedures is provided according to ISO standards; (3) a common functional unit, probably Energy Corrected Milk, should be used or assumed fat and protein content presented to enable comparisons; (4) where appropriate, site-specific emission factors and characterization factors should be used in environmental hotspots (e.g. manure management, spreading of synthetic fertilizer, production of purchased feed), and phosphorous loss should be better addressed; (5) a range of impact categories including climate change, energy use, land use, acidification and eutrophication should be used to assess pollution swapping, all of which are subject to national or regional directives; perhaps in the future biodiversity should also be included; and (6) the sensitivity to choices of methods and uncertainty of final results should be evaluated.

Preparation of highly dispersive and antioxidative nano zero-valent iron for the removal of hexavalent chromium.

In this study, carboxymethyl cellulose (CMC) was employed to stabilize zero-valent iron nanoparticles (CMC-nFe0) to improve their dispersity and antioxidation for enhanced hexavalent chromium (Cr(VI)) removal. Scanning electron microscope (SEM) observation revealed that the nFe0 agglomerated in clusters, while the CMC-nFe0 connected as chains and presented higher dispersity. Therefore, compared with 54% of the nFe0, the Cr(VI) removal rate of the CMC-nFe0 increased by 0.8 time, reaching 97%. Besides, the nFe0 precipitated in 1 d and was obviously oxidized within 7 d under anoxic condition, leading to a rapid decease of Cr(VI) removal efficiency from 54% to 3% in 56 d. In contrast, the CMC-nFe0 showed no obvious subsidence and oxidized phenomenon within 14 d, which retained a relatively high Cr(VI) removal efficiency of 63% in 56 d, contributing to effective blockage of dissolved oxygen infiltrating from solution to nFe0 particles in presence of CMC. After reaction, the valence state distribution of Cr between solution and material surface indicated that Cr(VI) reduction was dominant comparing to physical adsorption to particles in the remediation process conducted by CMC-nFe0. In addition, lower initial pH and higher iron dosage facilitated Cr(VI) removal. Those results indicated that the dispersive and antioxidative characteristics of CMC-nFe0 were significantly superior to those of nFe0, and CMC stabilization thereafter can be a promising method to promote Cr(VI) elimination by nFe0.

Nitrate mediated biotic zero valent iron corrosion for enhanced Cd(II) removal.

In this study, nitrate mediated biotic zero-valent iron (Fe0) corrosion was employed to enhance cadmium (Cd) removal from groundwater. In comparison with a 17.5% Cd(II) removal treated with abiotic Fe0, a 3.9 times higher Cd(II) removal of 86.2% was recorded in the nitrate-mediated biotic Fe0 system. Solids phase characterization confirmed that biogenic minerals such as green rust and iron sulfide could be formed in the nitrate-amended biotic Fe0 system, offering large amount of adsorption sites for Cd(II) removal. The decrease of nitrate concentration and the competition with cathodic hydrogen for biological nitrate reduction by extra organic substance such as sodium acetate both showed significant inhibition on Cd(II) removal, further proving that hydrogenotrophic denitrification was the main mechanism for enhanced Cd(II) removal. Besides, a relatively high Cd(II) removal efficiency was observed over a pH range of 5-8, and it increased with declining pH values. These results demonstrated that the bio-amended iron corrosion technology coupled Fe0-assisted H2 production with hydrogenotrophic denitrification exhibited excellent Cd(II) removal capacity, which enabled this technology a promising potential for Cd(II)-contaminated groundwater treatment and an alternative strategy for Cd(II) and nitrate co-contaminated groundwater remediation.

The apple DNA-binding one zinc-finger protein MdDof54 promotes drought resistance.

DNA-binding one zinc-finger (Dof) proteins constitute a family of transcription factors with a highly conserved Dof domain that contains a C2C2 zinc-finger motif. Although several studies have demonstrated that Dof proteins are involved in multiple plant processes, including development and stress resistance, the functions of these proteins in drought stress resistance are largely unknown. Here, we report the identification of the MdDof54 gene from apple and document its positive roles in apple drought resistance. After long-term drought stress, compared with nontransgenic plants, MdDof54 RNAi plants had significantly shorter heights and weaker root systems; the transgenic plants also had lower shoot and root hydraulic conductivity, as well as lower photosynthesis rates. By contrast, compared with nontransgenic plants, MdDof54-overexpressing plants had higher photosynthesis rates and shoot hydraulic conductivity under long-term drought stress. Moreover, compared with nontransgenic plants, MdDof54-overexpressing plants had higher survival percentages under short-term drought stress, whereas MdDof54 RNAi plants had lower survival percentages. MdDof54 RNAi plants showed significant downregulation of 99 genes and significant upregulation of 992 genes in response to drought, and 366 of these genes were responsive to drought. We used DAP-seq and ChIP-seq analyses to demonstrate that MdDof54 recognizes cis-elements that contain an AAAG motif. Taken together, our results provide new information on the functions of MdDof54 in plant drought stress resistance as well as resources for apple breeding aimed at the improvement of drought resistance.

Genome-wide identification of drought-responsive microRNAs in two sets of Malus from interspecific hybrid progenies.

Drought stress can negatively impact apple fruit quality and yield. Apple microRNAs (miRNAs) participate in apple tree and fruit development, as well as in biotic stress tolerance; however, it is largely unknown whether these molecules are involved in the drought response. To identify drought-responsive miRNAs in Malus, we first examined the drought stress tolerance of ten F1 progenies of R3 (M. × domestica) × M. sieversii. We performed Illumina sequencing on pooled total RNA from both drought-tolerant and drought-sensitive plants. The sequencing results identified a total of 206 known miRNAs and 253 candidate novel miRNAs from drought-tolerant plants and drought-sensitive plants under control or drought conditions. We identified 67 miRNAs that were differentially expressed in drought-tolerant plants compared with drought-sensitive plants under drought conditions. Under drought stress, 61 and 35 miRNAs were differentially expressed in drought-tolerant and drought-sensitive plants, respectively. We determined the expression levels of seven out of eight miRNAs by stem-loop qPCR analysis. We also predicted the target genes of all differentially expressed miRNAs and identified the expression of some genes. Gene Ontology analyses indicated that the target genes were mainly involved in stimulus response and cellular and metabolic processes. Finally, we confirmed roles of two miRNAs in apple response to mannitol. Our results reveal candidate miRNAs and their associated mRNAs that could be targeted for improving drought tolerance in Malus species, thus providing a foundation for understanding the molecular networks involved in the response of apple trees to drought stress.

A New Ethylene-Responsive Factor CaPTI1 Gene of Pepper (Capsicum annuum L.) Involved in the Regulation of Defense Response to Phytophthora capsici.

Ethylene-responsive factors (ERF) are usually considered to play diverse roles in plant response to biotic and abiotic stresses. In this study, an ERF gene CaPTI1 was isolated from pepper transcriptome database. CaPTI1 contains an open reading frame (ORF) of 543 bp, which encodes a putative polypeptide of 180 amino acids with a theoretical molecular weight of 20.30 kDa. Results of expression profile showed that CaPTI1 had a highest expression level in roots and this gene could not only response to the infection of Phytophthora capsici and the stresses of cold and drought, but also be induced by the signaling molecule (salicylic acid, Methyl Jasmonate, Ethephon, and hydogen peroxide). Furthermore, virus-induce gene silencing (VIGS) of CaPTI1 in pepper weakened the defense response significantly by reducing the expression of defense related genes CaPR1, CaDEF1 and CaSAR82 and also the root activity. These results suggested that CaPTI1 is involved in the regulation of defense response to P. capsici in pepper.