Arabidopsis SMO2 modulates ribosome biogenesis by maintaining the RID2 abundance during organ growth.

Ribosome biogenesis is a process of making ribosomes that is tightly linked with plant growth and development. Here, through a suppressor screen for the smo2 mutant, we found that lack of a ribosomal stress response mediator, ANAC082 partially restored growth defects of the smo2 mutant, indicating SMO2 is required for the repression of nucleolar stress. Consistently, the smo2 knock-out mutant exhibited typical phenotypes characteristic of ribosome biogenesis mutants, such as pointed leaves, aberrant leaf venation, disrupted nucleolar structure, abnormal distribution of rRNA precursors, and enhanced tolerance to aminoglycoside antibiotics that target ribosomes. SMO2 interacted with ROOT INITIATION DEFECTIVE 2 (RID2), a methyltransferase-like protein required for pre-rRNA processing. SMO2 enhanced RID2 solubility in Escherichia coli and the loss of function of SMO2 in plant cells reduced RID2 abundance, which may result in abnormal accumulation of FIBRILLARIN 1 (FIB1) and NOP56, two key nucleolar proteins, in high-molecular-weight protein complex. Taken together, our results characterized a novel plant ribosome biogenesis factor, SMO2 that maintains the abundance of RID2, thereby sustaining ribosome biogenesis during plant organ growth.

CbMYB108 integrates the regulation of diterpene biosynthesis and trichome development in Conyza blinii against UV-B.

Plants synthesize abundant terpenes through glandular trichomes (GTs), thereby protecting themselves from environmental stresses and increasing the economic value in some medicinal plants. However, the potential mechanisms for simultaneously regulating terpenes synthesis and GTs development remain unclear. Here, we showed that terpenes in Conyza blinii could be synthesized through capitate GTs. By treating with appropriate intensity of UV-B, the density of capitate GTs and diterpene content can be increased. Through analyzing corresponding transcriptome, we identified a MYB transcription factor CbMYB108 as a positive regulator of both diterpene synthesis and capitate GT density. Transiently overexpressing/silencing CbMYB108 on C. blinii leaves could increase diterpene synthesis and capitate GT density. Further verification showed that CbMYB108 upregulated CbDXS and CbGGPPS expression in diterpene synthesis pathway. Moreover, CbMYB108 could also upregulated the expression of CbTTG1, key WD40 protein confirmed in this study to promote GT development, rather than through interaction between CbMYB108 and CbTTG1 proteins. Thus, results showed that the UV-B-induced CbMYB108 owned dual-function of simultaneously improving diterpene synthesis and GT development. Our research lays a theoretical foundation for cultivating C. blinii with high terpene content, and broadens the understanding of the integrated mechanism on terpene synthesis and GT development in plants.

The transcription factor OsSPL9 endows rice with copper deficiency resilience.

Copper (Cu) is a crucial micronutrient essential for the growth and development of plants. Rice exhibits remarkable resistance to Cu deficiency, but the underlying molecular mechanisms are not well understood. In this study, we reveal that the plant's ability to withstand Cu deficiency is orchestrated by a transcription factor known as OsSPL9. We have demonstrated that OsSPL9 functions as a central regulator of Cu homeostasis. Disrupting OsSPL9 through knockout significantly reduces the plant's tolerance to Cu deficiency. As a result, the spl9 mutants exhibit reduced Cu accumulation in their shoots when compared to wild-type plants. This reduction is linked to a disruption in the transport of Cu from older leaves to younger ones. Furthermore, we show that OsSPL9 directly binds to GTAC motifs in the promoters of key genes involved in Cu uptake and transport, as well as Cu-miRNAs, and enhances their transcription under Cu-deficient conditions. Overall, our findings shed light on the molecular basis of rice resilience to Cu deficiency stress and place the transcription factor OsSPL9 as a master regulator of this response.

Effects of selenium nanoparticles produced by Lactobacillus acidophilus HN23 on lipid deposition in WRL68 cells.

Selenium is an essential trace element for most organisms, protecting cells from oxidative damage caused by free radicals and serving as an adjunctive treatment for non-alcoholic fatty liver disease (NAFLD). In this study, We used the lactic acid bacterium Lactobacillus acidophilus HN23 to reduce tetra-valent sodium selenite into particulate matter, and analyzed it through inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM), X-ray diffraction energy dispersive spectrometry (EDS), and Fourier transform infrared spectroscopy (FTIR). We found that it consisted of selenium nanoparticles (SeNPs) with a mass composition of 65.8 % zero-valent selenium and some polysaccharide and polypeptide compounds, with particle sizes ranging from 60 to 300 nm. We also detected that SeNPs were much less toxic to cells than selenite. We further used free fatty acids (FFA)-induced WRL68 fatty liver cell model to study the therapeutic effect of SeNPs on NAFLD. The results show that SeNPs are more effective than selenite in reducing lipid deposition, increasing mitochondrial membrane potential (MMP) and antioxidant capacity of WRL68 cells, which is attributed to the chemical valence state of selenium and organic composition in SeNPs. In conclusion, SeNPs produced by probiotics L. acidophilus had the potential to alleviate NAFLD by reducing hepatocyte lipid deposition and oxidative damage. This study may open a new avenue for SeNPs drug development to treat NAFLD.

SICKLE modulates lateral root development by promoting degradation of lariat intronic RNA.

Plant lateral roots (LRs) play vital roles in anchorage and uptake of water and nutrients. Here, we reveal that degradation of lariat intronic RNAs (lariRNAs) modulated by SICKLE (SIC) is required for LR development in Arabidopsis (Arabidopsis thaliana). Loss of SIC results in hyper-accumulation of lariRNAs and restricts the outgrowth of LR primordia, thereby reducing the number of emerged LRs. Decreasing accumulation of lariRNAs by over-expressing RNA debranching enzyme 1 (DBR1), a rate-limiting enzyme of lariRNA decay, restored LR defects in SIC-deficient plants. Mechanistically, SIC interacts with DBR1 and facilitates its nuclear accumulation, which is achieved through two functionally redundant regions (SIC1-244 and SIC252-319) for nuclear localization. Of the remaining amino acids in this region, six (SIC245-251) comprise a DBR1-interacting region while two (SICM246 and SICW251) are essential for DBR1-SIC interaction. Reducing lariRNAs restored microRNA (miRNA) levels and LR development in lariRNA hyper-accumulating plants, suggesting that these well-known regulators of LR development mainly function downstream of lariRNAs. Taken together, we propose that SIC acts as an enhancer of DBR1 nuclear accumulation by driving nuclear localization through direct interaction, thereby promoting lariRNA decay to fine-tune miRNA biogenesis and modulating LR development.

Citric Acid and Poly-glutamic Acid Promote the Phytoextraction of Cadmium and Lead in Solanum nigrum L. Grown in Compound Cd-Pb Contaminated Soils.

Phytoextraction is an efficient strategy for remediating heavy metal-contaminated soil. Chelators can improve the bioavailability of heavy metals and increase phytoextraction efficiency. However, traditional chelators have gradually been replaced due to secondary pollution. In this study, a typical organic acid (citric acid, CA) and a novel biodegradable chelator (poly-glutamic acid, PGA), were investigated using pot experiments to compare the phytoextraction efficiency of Solanum nigrum L. (a Cd (hyper)accumulator) for cadmium (Cd) and lead (Pb) in contaminated soil. The results showed CA and PGA significantly improved plant growth, and total Cd and Pb amounts of S. nigrum, both CA and PGA significantly increased the shoot Cd and Pb concentrations. However, only PGA significantly increased the root Pb concentration. CA and PGA application promoted the bioavailability of Cd and Pb in rhizosphere soils and their translocations from roots to shoots in S. nigrum. Both CA and PGA increased the phytoextraction efficiency of Cd and Pb in S. nigrum plants, and the PGA for Cd and Pb phytoextraction was more effective than CA. Our findings demonstrate that the biodegradable chelator PGA has great potential for enhancing phytoextraction from compound Cd-Pb contaminated soils, suggesting that biodegradable chelator-assisted phytoextraction with (hyper)accumulator is strongly recommended in severely contaminated sites.

A transporter for delivering zinc to the developing tiller bud and panicle in rice.

Tiller number is one of the most important agronomic traits that determine rice (Oryza sativa) yield. Active growth of tiller bud (TB) requires high amount of mineral nutrients; however, the mechanism underlying the distribution of mineral nutrients to TB with low transpiration is unknown. Here, we found that the distribution of Zn to TB is mediated by OsZIP4, one of the ZIP (ZRT, IRT-like protein) family members. The expression of OsZIP4 was highly detected in TB and nodes, and was induced by Zn deficiency. Immunostaining analysis revealed that OsZIP4 was mainly expressed in phloem of diffuse vascular bundles in the nodes and the axillary meristem. The mutation of OsZIP4 did not affect the total Zn uptake, but altered Zn distribution; less Zn was delivered to TB and new leaf, but more Zn was retained in the basal stems at the vegetative growth stage. Bioimaging analysis showed that the mutant aberrantly accumulated Zn in enlarged and transit vascular bundles of the basal node, whereas in wild-type high accumulation of Zn was observed in the meristem part. At the reproductive stage, mutation of OsZIP4 resulted in delayed panicle development, which is associated with decreased Zn distribution to the panicles. Collectively, OsZIP4 is involved in transporting Zn to the phloem of diffuse vascular bundles in the nodes for subsequent distribution to TBs and other developing tissues. It also plays a role in transporting Zn to meristem cells in the TBs.

OsbHLH061 links TOPLESS/TOPLESS-RELATED repressor proteins with POSITIVE REGULATOR OF IRON HOMEOSTASIS 1 to maintain iron homeostasis in rice.

As excess iron (Fe) is toxic, uptake of this essential micronutrient must be tightly controlled. Previous studies have shown that Oryza sativa (rice) POSITIVE REGULATOR OF IRON HOMEOSTASIS1 (OsPRI1) acts upstream of the iron-related transcription factor 2 (OsIRO2) and OsIRO3 to positively regulate root-to-shoot Fe translocation. However, as expression of OsPRI1 is constitutive it is unclear how the Fe-deficiency response is turned off to prevent toxicity when Fe is sufficient. The bHLH transcription factor OsbHLH061 interacts with OsPRI1, and this study used molecular, genetics, biochemical and physiological approaches to functionally characterise OsbHLH061 and how it affects Fe homeostasis. OsbHLH061 knockout or overexpression lines increase or decrease Fe accumulation in shoots respectively. Mechanistically, OsbHLH061 expression is upregulated by high Fe, and physically interacts with OsPRI1, the OsbHLH061-OsPRI1 complex recruits TOPLESS/TOPLESS-RELATED (OsTPL/TPR) co-repressors to repress OsIRO2 and OsIRO3 expression. The OsbHLH061 ethylene-responsive element-binding factor-associated amphiphilic repression (EAR) motif is required for this transcriptional repression activity. These results define a functional OsTPL/TPR-OsbHLH061-OsPRI1-OsIRO2/3 module that negatively controls long-distance transport of Fe in plants for adaptation to changing Fe environments and maintain Fe homeostasis in rice.

Genetic and epigenetic variation separately contribute to range expansion and local metalliferous habitat adaptation during invasions of Chenopodium ambrosioides into China.

BACKGROUND AND AIMS: Invasive plants often colonize wide-ranging geographical areas with various local microenvironments. The specific roles of epigenetic and genetic variation during such expansion are still unclear. Chenopodium ambrosioides is a well-known invasive alien species in China that can thrive in metalliferous habitats. This study aims to comprehensively understand the effects of genetic and epigenetic variation on the successful invasion of C. ambrosioides. METHODS: We sampled 367 individuals from 21 heavy metal-contaminated and uncontaminated sites with a wide geographical distribution in regions of China. We obtained environmental factors of these sampling sites, including 13 meteorological factors and the contents of four heavy metals in soils. Microsatellite markers were used to investigate the demographic history of C. ambrosioides populations in China. We also analysed the effect of epigenetic variation on metalliferous microhabitat adaptation using methylation-sensitive amplified polymorphism (MSAP) markers. A common garden experiment was conducted to compare heritable phenotypic variations among populations. KEY RESULTS: Two distinct genetic clusters that diverged thousands of years ago were identified, suggesting that the eastern and south-western C. ambrosioides populations in China may have originated from independent introduction events without recombination. Genetic variation was shown to be a dominant determinant of phenotypic differentiation relative to epigenetic variation, and further affected the geographical distribution pattern of invasive C. ambrosioides. The global DNA unmethylation level was reduced in metalliferous habitats. Dozens of methylated loci were significantly associated with the heavy metal accumulation trait of C. ambrosioides and may contribute to coping with metalliferous microenvironments. CONCLUSIONS: Our study of C. ambrosioides highlighted the dominant roles of genetic variation in large geographical range expansion and epigenetic variation in local metalliferous habitat adaptation.

Physiological and transcriptional responses of the ectomycorrhizal fungus Cenococcum geophilum to salt stress.

Ectomycorrhizal (ECM) fungi improve the host plant's tolerance to abiotic and biotic stresses. Cenococcum geophilum (Cg) is among the most common ECM fungi worldwide and often grows in saline environments. However, the physiological and molecular mechanisms of salt tolerance in this fungus are largely unknown. In the present study, 12 isolates collected from different ecogeographic regions were used to investigate the mechanism of salt tolerance of Cg. The isolates were classified into four groups (salt-sensitive, moderately salt-tolerant, salt-tolerant, and halophilic) based on their in vitro mycelial growth under 0, 50, 125, 250, and 500 mM NaCl concentrations. Hence, the Na, Ca, P, and K concentrations of mycelia and the pH of the culture solution were determined. Compared with salt-tolerant isolates, treatment with 250 mM NaCl significantly increased the sodium concentration and decreased the potassium concentration of salt-sensitive isolates. RNA-sequencing and qRT-PCR analysis were conducted to identify differentially expressed genes (DEGs) involved in transmembrane transport and oxidoreductase activity pathways. The hydrogen peroxide concentration and activities of peroxidase and superoxide dismutase in mycelia were determined, and the accumulation and scavenging of reactive oxygen species in the salt-sensitive isolates were more active than those in the salt-tolerant isolates. The results supply functional validations to RNA-seq and qRT-PCR analysis. This study provides novel insights into the salt-stress response of Cg isolates and provides a foundation for elucidation of the salt-tolerance mechanism of ECM fungi.

Remediation of copper-contaminated soils using Tagetes patula L., earthworms and arbuscular mycorrhizal fungi.

Arbuscular mycorrhizal fungi (AMF) and earthworms have potential uses in the bioremediation of contaminated soils. In recent years, heavy metal-contaminated sites have been remediated by adding plants and AMF or earthworms to the soil. However, there are few studies on remediation using combinations of plants, animals, and microbes, especially for the remediation of Cu-contaminated soil. The present study investigated the separate and combined effects of AMF and earthworms on Cu-contaminated soil in which Tagetes patula L. was grown. The results show that the combined application of AMF and earthworms markedly increased the biomass of plant shoots and roots by more than 100%. It also increased Cu extraction by T. patula by 270%. The combined treatment was effective in increasing the CEC, contents of OM, and available Cu, P and K, but reduced the soil pH. Furthermore, the combined treatment significantly increased the abundance and diversity of the soil microbial community. In particular, the abundances of the bacteria Bacteroides, Proteobacteria, and Actinobacteria were increased, with the genera Flavobacterium, Pedobacter, Algoriphagus, Gaetbulibacter, Pseudomonas, Luteimonas, and Arthrobacter dominating. Meanwhile, the abundance of the fungus Zygomycota was increased, with Mortierella dominating. Moreover, inoculation with earthworms greatly improved the structure of the soil microbial community.

Compared with phytoremediation or microbial remediation alone, combined remediation was considered to be a more efficient remediation strategy. This study describes the effects of the combined remediation of T. patula, AMF, and earthworms on the physiochemical properties and microbial community of Cu-contaminated soil. This provides a comprehensive strategy to improve the phytoremediation efficiency in Cu-contaminated soil.

A meta-analysis about the accumulation of heavy metals uptake by Sedum alfredii and Sedum plumbizincicola in contaminated soil.

Sedum alfredii and Sedum plumbizincicola typically have high heavy metal (such as Zn and Cd) accumulation capacities with fast growth rates and relatively high Pb tolerance in contaminated soils. We compared the accumulation characteristics of heavy metals in Sedum species through meta-analysis. Furthermore, we analyzed the effects of soil organic matter (SOM) and soil pH on Cd, Pb and Zn accumulation by S. alfredii and S. plumbizincicola and the correlation between various metals. Results showed that the accumulations of Cd and Zn in shoots were higher than that of roots, but Pb accumulated in roots more than shoots. Moreover, there is a significant positive correlation between the accumulation of Zn and Cd in shoots. We found that the heavy metal accumulation rate in shoots was higher with lower soil pH. Sedum species had the highest Cd adsorption capacity in 20-30 g/kg SOM and the highest Zn adsorption capacity in SOM less than 20 g/kg. The accumulation rate of Cd in shoots of S. plumbizincicola was increased with exposure time, while the accumulation rate of Zn was slightly decreased.

S. alfredii and S. plumbizincicola are two common Cd and Zn hyperaccumulators. We systematically compared the accumulation characteristics of heavy metals in Sedum plants and the effects of soil organic matter and pH on the accumulation of Cd, Pb and Zn in S. alfredii and S. plumbizincicola through meta-analysis. This provides certain theoretical knowledge for the application of sedum plants to the phytoremediation of heavy metal contaminated soils.

The pentatricopeptide repeat protein GEND1 is required for root development and high temperature tolerance in Arabidopsis thaliana.

Pentatricopeptide repeat (PPR) proteins are a large family in land plants that play a role in organellular RNA processing, editing, and splicing. Here, we identify an Arabidopsis thaliana mutant, gend1-1, which exhibits a short root phenotype with reduced meristem size and cell numbers. Positional cloning of GEND1 revealed that it encodes a PPR protein, and functional analysis showed that GEND1 can bind and edit mitochondrial ccmFn-1 mRNA, causing gend1 mutants to have decreased levels of cytochrome C. GEND1 was up-regulated by high temperature conditions, to which gend1 mutants were hypersensitive. Analysis of a set of PPR mutants under high temperature showed that mutants with defects in cytochrome C had comparable temperature sensitivity to gend1. Collectively, these results suggest that cytochrome C plays an important role in root development and high temperature response in Arabidopsis.

Alternative Splicing Plays a Critical Role in Maintaining Mineral Nutrient Homeostasis in Rice (Oryza sativa).

Alternative splicing (AS) of pre-mRNAs promotes transcriptome and proteome diversity and plays important roles in a wide range of biological processes. However, the role of AS in maintaining mineral nutrient homeostasis in plants is largely unknown. To clarify this role, we obtained whole transcriptome RNA sequencing data from rice (Oryza sativa) roots grown in the presence or absence of several mineral nutrients (Fe, Zn, Cu, Mn, and P). Our systematic analysis revealed 13,291 alternatively spliced genes, representing ∼53.3% of the multiexon genes in the rice genome. As the overlap between differentially expressed genes and differentially alternatively spliced genes is small, a molecular understanding of the plant's response to mineral deficiency is limited by analyzing differentially expressed genes alone. We found that the targets of AS are highly nutrient-specific. To verify the role of AS in mineral nutrition, we characterized mutants in genes encoding Ser/Arg (SR) proteins that function in AS. We identified several SR proteins as critical regulators of Zn, Mn, and P nutrition and showed that three SR protein-encoding genes regulate P uptake and remobilization between leaves and shoots of rice, demonstrating that AS has a key role in regulating mineral nutrient homeostasis in rice.

Phytotoxicity and accumulation of Cu in mature and young leaves of submerged macrophyte Hydrilla verticillata (L.f.) Royle.

Phytotoxicity and accumulation of Cu in mature and young leaves of submerged macrophyte Hydrilla verticillata (L.f.) Royle were investigated by analyzing the chlorophyll contents, chloroplast ultrastructure and leaf surface structure under different Cu treatments (0, 0.01, 0.05 and 0.1 f mg L-1). The results showed that 0.05 and 0.1 mg L-1 Cu treatment decreased the contents of Chl a and Chl b, and caused damage on leaf surface structure and chloroplast ultrastructure compared with control (0 mg L-1 Cu treatment). Higher concentration of Cu induced Chlorophyll decreases and the damages on the leaf surface structure and chloroplast ultrastructure were more pronounced in mature than in young leaves. It was observed that leaf Cu concentration increased almost linearly with exposure time and majority of the Cu accumulated in the cell walls. Among different cell wall fractions, the majority of Cu accumulated in cell walls was bound to the hemicellulose 1 and cellulose, followed by the pectin, hemicellulose 2. Mature leaves had significantly higher the concentrations of total Cu and bound-Cu in cell walls due to higher uronic acid content in their cell wall fractions (pectin, hemicellulose 1 and cellulose) than young leaves. Distinct cell wall composition might partially contribute to the different Cu toxicity and accumulation between mature and young leaves of submerged macrophyte H. verticillata. Our results show that mature leaves are more efficient in the uptake and accumulation of Cu than young leaves, which might explain why mature leaves sustain more severe damage.

Evaluation of biogas production potential of trace element-contaminated plants via anaerobic digestion.

Within the domain of phytoremediation research, the proper disposal of harvestable plant parts, that remove pollutants from contaminated soil, has been attracted extensive attention. Here, the bioenergy generation capability of trace metals (Cu, Pb, Zn, Cd, Mn, and As) polluted plants was assessed. The biogas production potential of accumulators or hyperaccumulator plants, Elsholtzia haichowensis, Sedum alfredii, Solanum nigrum, Phytolacca americana and Pteris vittata were 259.2 ± 1.9, 238.7 ± 4.2, 135.9 ± 0.9, 129.5 ± 2.9 and 106.8 ± 2.1 mL/g, respectively. The presence of Cu (at approximately 1000 mg/kg) increased the cumulative biogas production, the daily methane production and the methane yield of E. haichowensis. For S. alfredii, the presence of Zn (≥500 mg/kg) showed a significant negative impact on the methane content in biogas, and the daily methane production, which decreased the biogas and methane yield. The biogas production potential increased when the content of Mn was at 5 000-10,000 mg/kg, subsequently, decreased when the value of Mn at 20,000 mg/kg. However, Cd (1-200 mg/kg), Pb (125-2000 mg/kg) and As (1250-10,000 mg/kg) showed no distinctive change in the cumulative biogas production of S. nigrum, S. alfredii and P. vittata, respectively. The methane yield showed a strong positive correlation (R2 =0.9704) with cumulative biogas production, and the energy potential of the plant residues were at 415-985 kWh/ton. Thus, the anaerobic digestion has bright potential for the disposal of trace metal contaminated plants, and has promising prospects for the use in energy production.

Analysis of the long-term effectiveness of biochar immobilization remediation on heavy metal contaminated soil and the potential environmental factors weakening the remediation effect: A review.

Currently, the research and application of biochar in the remediation of heavy metal contaminated soil has become a hotspot, especially regarding the remediation of agricultural land. Biochar has been proved to be effective in reducing the content of available heavy metals in the soil as well as the heavy metals in plants. However, the long-term effectiveness of biochar immobilization has not been widely studied. In this review, retrospective search was carried out on the published literature results concerning remediation effects of biochar on different areas of heavy metal contaminated soil in the recent years, its application in field remediation (several years), and some potential abiotic and biotic factors that may weaken the immobilization effects of biochar. This results indicate that: (1) biochar is widely used in the remediation of heavy metal contaminated soil in different areas and has excellent immobilization effect. (2) Most of the research demonstrate that the immobilization effect of biochar is effective for 2-3 years or according to few results even for 5 years. However, there have been various reports claiming that the immobilization effect of biochar decreases with time. (3) Abiotic factors such as acid rain, flooded environment, changes in soil condition (pH, redox and dissolved organic matter) and changes in biochar (Cl- and alkali leaching) can significantly weaken the immobilization effect of biochar. (4) Biotic factors such as plant roots, earthworms and soil microorganisms can also significantly reduce the immobilization effect of biochar. Therefore, field experiments having longer time span with biochar need to be further carried out, and the developmental research of modified biochar with a more stable immobilization effect also needs further attention.

Promotion of Zinc Tolerance, Acquisition and Translocation of Phosphorus in Mimosa pudica L. Mediated by Arbuscular Mycorrhizal Fungi.

Heavy metal contamination of soil is of increasing concern because of its potential risk to human health. In this study, two AMFs (Rhizophagus intraradices and Funneliformis mosseae) substantially increased the biomass of bashfulgrass in Zn-contaminated soil, even at Zn levels of up to 600 mg kg-1. Zn uptake in R. intraradices- and F. mosseae-mycorrhizal bashfulgrass was increased by 40-fold and 7-fold, respectively, when plants grown in Zn-contaminated (400 mg kg-1) soil. Elemental analysis showed that neither AMF had an effect on Zn concentration in plant tissues, including the roots and shoots. However, a significant increase of phosphorus (P) concentration was observed, suggesting the increased is from the improved use efficiency of soil nutrients by AMFs. Comparing the two AMFs, better growth performance with more biomass occurred with R. intraradices-inoculated bashfulgrass in Zn-contaminated soil. This is consistent with R. intraradices being more tolerant to Zn than F. mosseae, indicated by a higher colonization percentage in bashfulgrass roots. Taken together, our data indicate that AMFs possibly improve acquisition and translocation of P to promote increased biomass. Moreover, mycorrhiza did not enhance Zn accumulation in shoots and roots of bashfulgrass at the same Zn level. In the future, developing AMF (especially R. intraradices) inoculation of plants might be a desirable means of safe production of ornamental plants in metal-polluted soil.

Excess copper inhibits the growth of rice seedlings by decreasing uptake of nitrate.

Copper (Cu) toxicity has a deleterious effect on plant growth, and different nitrogen (N) forms have significantly different impacts on the uptake and accumulation of heavy metals by plants. However, it remains unclear how excess Cu inhibits the growth of rice seedlings under different N forms. Here, we examined the mechanism of Cu toxicity inhibiting the growth of rice supplied with different N forms. Rice seedlings were grown in a nutrient solution with 0.81 mmol L-1 N, as ammonium (NH4+), nitrate (NO3-) and NH4+ + NO3-, or without N (0 N) in the presence of 0.2 µmol L-1 CuSO4 or 10 µmol L-1 CuSO4. The inhibition of shoot growth under excess Cu was more pronounced in plants that were supplied with NO3- than NH4+; such inhibition was not induced by higher Cu concentration in shoots. Applied with NO3- alone increased solution pH value up to 6.2, but supplied with NH4+ alone and NH4+ + NO3- decreased solution pH value to 4.0 and 4.2, respectively. The increment of solution pH reduced Cu concentration in shoots of rice supplied with NO3- alone. Copper toxicity decreased NO3- concentrations in rice seedlings that were supplied with NO3- alone but increased the NH4+ concentrations in plants that were supplied with NH4+ or NH4+ + NO3-. High Cu levels reduced the uptake of NO3- in roots by the analysis of net NO3- flux and NO3- assimilation enzymes activity. Under excess Cu, the transcript levels of OsNPF6.5, OsNPF2.2 and OsNPF2.4 genes were suppressed, while OsNRT2.1, OsNRT2.2 and OsNAR2.1 were raised in roots. In conclusion, Cu toxicity inhibits NO3- uptake and upward translocation by modulating the expression level of NO3- transporter genes. The reduction in the concentrations of NO3- and total N decreased shoot growth of rice seedlings when N was supplied as NO3-. Hence, rice seedlings supplied with NO3- had lower shoot biomass than those with NH4+ under Cu stress.

Comparative transcriptomic analysis reveals novel insights into the response to Cr(VI) exposure in Cr(VI) tolerant ectomycorrhizal fungi Pisolithus sp. 1 LS-2017.

Chromium (Cr) is one of the most toxic heavy metals and a health hazard to millions of people worldwide. Ectomycorrhizal (ECM) fungi can assist plants in phytoremediation of heavy metal contaminated soil. Cr tolerance differs among ECM fungal varieties, but the underlying molecular mechanisms of Cr tolerance in ECM fungi are not clear. This study identified, analysed and compared the Cr(VI)-induced transcriptional changes between Cr(VI)-tolerant strain (Pisolithus sp. 1 LS-2017) and Cr(VI)-sensitive strain (Pisolithus sp. 2 LS-2017) by de novo transcriptomic analysis. The results showed that 93,642 assembled unique transcripts representing the 22,353 (46.76%) unigenes matched the proteins we have known in the Nr database and 47,801 unigenes were got from the Pisolithus spp. For DEGs between the control and 10 mg/L Cr(VI) treatment, cyanoamino acid metabolic, type I diabetes mellitus metabolism, nitrogen metabolism and beta-Alanine metabolism pathways were significantly enriched (p < 0.05) in Pisolithus sp. 1 LS-2017. Two nitrate reductase family genes (nidD, niiA) provide Cr(VI) tolerance for Pisolithus sp. 1 LS-2017 by regulating Cr(VI) reduction. In addition, NO produced by nidD, niiA regulated denitrification can alleviate Cr(VI) induced oxidative stress. In Pisolithus sp. 2 LS-2017, the alcC, aldA and lcf2 gene may alleviate Cr(VI) induced oxidative stress by protecting SH groups and increasing secondary metabolism, reducing detoxify aldehydes to carboxylic acids and producing LCPUFAs respectively; .T gene regulate Cr(VI) induced wound healing by pigmentation and stability of melanin in spore; MKP2 gene accelerate Cr(VI) induced cell death and gpmA gene regulated Cr(VI) induced energy emergency.