Differential responses of root growth, acid invertase activity and transcript level to copper stress in two contrasting populations of Elsholtzia haichowensis

In Vitro Inducted Tetraploid Elsholtzia splendens Nakai ex F. Maek. Alters Polyphenol Species and Synthesis

Elsholtzia splendens Nakai ex F. Maek. has been employed in traditional Chinese medicine for millennia. Nevertheless, the small size and the paucity of research on its pharmacological effects have restricted its extensive utilisation in clinical medicine. Polyploid breeding represents an effective method for the rapid enhancement of plant biomass and metabolites. In this study, the most effective in vitro method for inducing tetraploid formation was identified as axillary buds treated in a solution of colchicine at a concentration of 1% for 24 h. Meanwhile, a comparison between tetraploids and diploids yielded two significant findings: (1) The presence of 6-zonocolpate and 8-zonocolpate pollen grains can be used as distinguishing characteristics for diploid and tetraploid, respectively. (2) Genome duplication resulted in alterations to the polyphenol species and synthesis pathway in E. splendens. The accumulation of wogonin, oroxylin A, baicalin, chrysin, acacetin and related derivatives was markedly greater in tetraploid plants, whereas apigenin, naringenin, scutellarein and related derivatives were found to accumulate to a greater extent in diploid plants. It is noteworthy that wogonin and oroxylin A were uniquely detected in tetraploids, indicating that the generated tetraploids may harbor novel pharmacological value. The findings not only provided new insights into the metabolic mechanism of polyploidisation but also established a foundation for the selection and breeding of novel genetic resources of E. splendens.

Comparison and Characterization of a Cell Wall Invertase Promoter from Cu-Tolerant and Non-Tolerant Populations of Elsholtzia haichowensis

Cell wall invertase (CWIN) activity and the expression of the corresponding gene were previously observed to be significantly elevated in a Cu-tolerant population of Elsholtzia haichowensis relative to a non-tolerant population under copper stress. To understand the differences in CWIN gene regulation between the two populations, their CWIN promoter β-glucuronidase (GUS) reporter vectors were constructed. GUS activity was measured in transgenic Arabidopsis in response to copper, sugar, and phytohormone treatments. Under the copper treatment, only the activity of the CWIN promoter from the Cu-tolerant population was slightly increased. Glucose and fructose significantly induced the activity of CWIN promoters from both populations. Among the phytohormone treatments, only salicylic acid induced significantly higher (p < 0.05) activity of the Cu-tolerant CWIN promoter relative to the non-tolerant promoters. Analysis of 5′-deletion constructs revealed that a 270-bp promoter fragment was required for SA induction of the promoter from the Cu-tolerant population. Comparison of this region in the two CWIN promoters revealed that it had 10 mutation sites and contained CAAT-box and W-box cis-elements in the Cu-tolerant promoter only. This work provides insights into the regulatory role of SA in CWIN gene expression and offers an explanation for differences in CWIN expression between E. haichowensis populations.

Uptake and translocation of perfluoroalkyl acids with different carbon chain lengths (C2-C8) in wheat (Triticum acstivnm L.) under the effect of copper exposure

The co-contamination by perfluoroalkyl acids (PFAAs) and heavy metals (HMs) is ubiquitous in the surface environment subjected to sewage irrigation and land application of sludge. However, the joint effects of HMs and PFAAs on plant roots are not well clarified. This study explored the root uptake and acropetal translocation behaviors of C2-C8 PFAAs by wheat (Triticum acstivnm L.) under the co-exposure of copper (Cu). The underlying uptake mechanisms of PFAAs were verified in a defective root system. The results showed that excessive Cu (100-400 μmol/L) damaged the cell membrane of wheat root to increase electrolytic leakage. In the defective root system, the root concentrations of PFAAs decreased by 6%-73% and the decrease rates were negatively associated with the carbon chain length of PFAAs. Along with the decrease in root concentrations of PFAAs, the amount of ultrashort-chain (C2-C3) and short-chain (C4-C6) PFAAs translocated to the shoot also decreased by 45%-84%. In contrast, the acropetal translocation of long-chain (C8) PFAAs, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), was enhanced under Cu exposure due to the increase in root permeability as observed by increased electrolytic leakage. The shoot concentrations of PFOA and PFOS under Cu exposure were up to 5.5 and 11 times higher than those in the control, respectively. These results suggested that PFOA and PFOS could enter wheat root more easily through the breaks caused by Cu exposure and thereby their acropetal transportation to shoot was enhanced. Therefore, the risk of plant accumulation of long-chain PFAAs can be potentially underestimated if without considering the co-contamination with HMs in the environment.

Copper bioavailability, uptake, toxicity and tolerance in plants: A comprehensive review

Copper (Cu) is an essential element for humans and plants when present in lesser amount, while in excessive amounts it exerts detrimental effects. There subsists a narrow difference amid the indispensable, positive and detrimental concentration of Cu in living system, which substantially alters with Cu speciation, and form of living organisms. Consequently, it is vital to monitor its bioavailability, speciation, exposure levels and routes in the living organisms. The ingestion of Cu-laced food crops is the key source of this heavy metal toxicity in humans. Hence, it is necessary to appraise the biogeochemical behaviour of Cu in soil-plant system with esteem to their quantity and speciation. On the basis of existing research, this appraisal traces a probable connexion midst: Cu levels, sources, chemistry, speciation and bioavailability in the soil. Besides, the functions of protein transporters in soil-plant Cu transport, and the detrimental effect of Cu on morphological, physiological and nutrient uptake in plants has also been discussed in the current manuscript. Mechanisms related to detoxification strategies like antioxidative response and generation of glutathione and phytochelatins to combat Cu-induced toxicity in plants is discussed as well. We also delimits the Cu accretion in food crops and allied health perils from soils encompassing less or high Cu quantity. Finally, an overview of various techniques involved in the reclamation and restoration of Cu-contaminated soils has been provided.

TPST is involved in fructose regulation of primary root growth in Arabidopsis thaliana

TPST is involved in fructose signaling to regulate the root development and expression of genes in biological processes including auxin biosynthesis and accumulation in Arabidopsis. Sulfonation of proteins by tyrosine protein sulfotransferases (TPST) has been implicated in many important biological processes in eukaryotic organisms. Arabidopsis possesses a single TPST gene and its role in auxin homeostasis and root development has been reported. Here we show that the Arabidopsis tpst mutants are hypersensitive to fructose. In contrast to sucrose and glucose, fructose represses primary root growth of various ecotypes of Arabidopsis at low concentrations. RNA-seq analysis identified 636 differentially expressed genes (DEGs) in Col-0 seedlings in response to fructose verses glucose. GO and KEGG analyses of the DEGs revealed that fructose down-regulates genes involved in photosynthesis, glucosinolate biosynthesis and IAA biosynthesis, but up-regulates genes involved in the degradation of branched amino acids, sucrose starvation response, and dark response. The fructose responsive DEGs in the tpst mutant largely overlapped with that in Col-0, and most DEGs in tpst displayed larger changes than in Col-0. Interestingly, the fructose up-regulated DEGs includes genes encoding two AtTPST substrate proteins, Phytosulfokine 2 (PSK2) and Root Meristem Growth Factor 7 (RGF7). Synthesized peptides of PSK-α and RGF7 could restore the fructose hypersensitivity of tpst mutant plants. Furthermore, auxin distribution and accumulation at the root tip were affected by fructose and the tpst mutation. Our findings suggest that fructose serves as a signal to regulate the expression of genes involved in various biological processes including auxin biosynthesis and accumulation, and that modulation of auxin accumulation and distribution in roots by fructose might be partly mediated by the TPST substrate genes PSK-α and RGF7.

Identification and Immobilization of an Invertase With High Specific Activity and Sucrose Tolerance Ability of Gongronella sp. w5 for High Fructose Syrup Preparation

Invertases catalyze the hydrolysis of sucrose into fructose and glucose and can be employed as an alternative in producing high fructose syrup. In this study, we reported the heterologous expression of an invertase gene (GspInv) of Gongronella sp. w5 in Komagataella pastoris. GspInv activity reached 147.6 ± 0.4 U/mL after 5 days of methanol induction. GspInv is invertase with a high specific activity of 2,776.1 ± 124.2 U/mg toward sucrose. GspInv showed high tolerance to sucrose (IC 5 0 = 1.2 M), glucose (IC 5 0 > 2 M), fructose (IC 5 0 = 1.5 M), and a variety of metal ions that make it an ideal candidate for high fructose syrup production. A carbohydrate-binding module was sequence-optimized and fused to the N-terminus of GspInv. The fusion protein had the highest immobilization efficiency at room temperature within 1 h adsorption, with 1 g of cellulose absorption up to 8,000 U protein. The cellulose-immobilized fusion protein retained the unique properties of GspInv. When applied in high fructose syrup preparation by using 1 M sucrose as the substrate, the sucrose conversion efficiency of the fused protein remained at approximately 95% after 50 h of continuous hydrolysis on a packed bed reactor. The fused protein can also hydrolyze completely the sucrose in sugarcane molasses. Our results suggest that GspInv is an unusual invertase and a promising candidate for high fructose syrup preparation.

Heavy Metal Exposure Alters the Uptake Behavior of 16 Priority Polycyclic Aromatic Hydrocarbons (PAHs) by Pak Choi ( Brassica chinensis L.)

Polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) are predominant pollutants normally coexisting at electronic waste dumping sites or in agricultural soils irrigated with wastewater. The accumulation of PAHs and HMs in food crops has become a major concern for food security. This study explored the hydroponic uptake of 16 priority PAHs and 5 HMs (Cd, Cr, Cu, Pb, and Zn) by pak choi ( Brassica chinensis L.). PAHs exhibited stronger inhibition on pak choi growth and physiological features than HMs. Five HMs were categorized into high-impact HMs (Cr, Cu, and Pb) and low-impact HMs (Cd and Zn) with distinct behavior under the coexposure with PAHs, and low-impact HMs showed synergistic toxicity effects with PAHs. Coexposure to PAHs and HMs slightly decreased the uptake and translocation of PAHs by pak choi, possibly attributing to the commutative hindering effects on root adsorption or cation-π interactions. The bioconcentration factors in PAHs + HMs treatments were independent of the octanol-water partition coefficient ( K_ow), owing to the cation-π interaction associated change of K_ow and induced defective root system. This study provides new insights into the mechanisms and influential factors of PAHs uptake in Brassica chinensis L. and gives clues for reassessing the environmental risks of PAHs in food crops.

Impacts of environmental factors on the whole microbial communities in the rhizosphere of a metal-tolerant plant: Elsholtzia haichowensis Sun

Rhizospheric microbes play important roles in plant growth and heavy metals (HMs) transformation, possessing great potential for the successful phytoremediation of environmental pollutants. In the present study, the rhizosphere of Elsholtzia haichowensis Sun was comprehensively studied to uncover the influence of environmental factors (EFs) on the whole microbial communities including bacteria, fungi and archaea, via quantitative polymerase chain reaction (qPCR) and high-throughput sequencing. By analyzing molecular ecological network and multivariate regression trees (MRT), we evaluated the distinct impacts of 37 EFs on soil microbial community. Of them, soil pH, HMs, soil texture and nitrogen were identified as the most influencing factors, and their roles varied across different domains. Soil pH was the main environmental variable on archaeal and bacterial community but not fungi, explaining 25.7%, 46.5% and 40.7% variation of bacterial taxonomic composition, archaeal taxonomic composition and a-diversity, respectively. HMs showed important roles in driving the whole microbial community and explained the major variation in different domains. Nitrogen (NH₄-N, NO₃-N, NO₂-N and TN) explained 47.3% variation of microbial population composition and 15.9% of archaeal taxonomic composition, demonstrating its influence in structuring the rhizospheric microbiome, particularly archaeal and bacterial community. Soil texture accounted for 10.2% variation of population composition, 28.9% of fungal taxonomic composition, 19.2% of fungal a-diversity and 7.8% of archaeal a-diversity. Rhizosphere only showed strong impacts on fungi and bacteria, accounting for 14.7% and 4.9% variation of fungal taxonomic composition and bacterial a-diversity. Spatial distance had stronger influence on bacteria and archaea than fungi, but not as significant as other EFs. For the first time, our study provides a complete insight into key influential EFs on rhizospheric microbes and how their roles vary across microbial domains, giving a hand for understanding the construction of microbial communities in rhizosphere.

Differential expression of vacuolar and defective cell wall invertase genes in roots and seeds of metalliferous and non-metalliferous populations of Rumex dentatus under copper stress

Acid invertase activities in roots and young seeds of a metalliferous population (MP) of Rumex dentatus were previously observed to be significantly higher than those of a non-metalliferous population (NMP) under Cu stress. To date, no acid invertase gene has been cloned from R. dentatus. Here, we isolated four full-length cDNAs from the two populations of R. dentatus, presumably encoding cell wall (RdnCIN1 and RdmCIN1 from the NMP and MP, respectively) and vacuolar invertases (RdnVIN1 and RdmVIN1 from the NMP and MP, respectively). Unexpectedly, RdnCIN1 and RdmCIN1 most likely encode special defective invertases with highly attenuated sucrose-hydrolyzing capacity. The transcript levels of RdmCIN1 were significantly higher than those of RdnCIN1 in roots and young seeds under Cu stress, whereas under control conditions, the former was initially lower than the latter. Unexpected high correlations were observed between the transcript levels of RdnCIN1 and RdmCIN1 and the activity of cell wall invertase, even though RdnCIN1 and RdmCIN1 do not encode catalytically active invertases. Similarly, the transcript levels of RdmVIN1 in roots and young seeds were increased under Cu stress, whereas those of RdnVIN1 were decreased. The high correlations between the transcript levels of RdnVIN1 and RdmVIN1 and the activity of vacuolar invertase indicate that RdnVIN1 and RdmVIN1 might control distinct vacuolar invertase activities in the two populations. Moreover, a possible indirect role for acid invertases in Cu tolerance, mediated by generating a range of sugars used as nutrients and signaling molecules, is discussed.

Heterologous expression and comparative characterization of vacuolar invertases from Cu-tolerant and non-tolerant populations of Elsholtzia haichowensis

Vacuolar invertases (VINs) from Cu-tolerant and non-tolerant populations of Elsholtzia haichowensis have similar enzyme properties, and the enzyme protein divergences contribute little to the varied VIN activities between the contrasting populations. In our previous studies of Elsholtzia haichowensis, vacuolar invertase (VIN) activity in roots of a Cu-tolerant population was found to be significantly higher than that of a non-tolerant population under Cu stress. Divergences of amino acid residues in a sucrose-binding box and other regions of the VINs were detected. To test whether the amino acid divergences influence the enzyme properties of VINs, and thus are relevant to the differences in enzyme activities between the contrasting populations of E. haichowensis, two VIN genes from the Cu-tolerant population (EhCvINV) and non-tolerant population (EhNvINV) were heterologously expressed in Pichia pastoris, and the enzyme properties of the recombinants were characterized and compared. Both of the recombinant enzymes showed temperature optima of 70 °C and pH optima of 4.5-5.5. Copper as well as other heavy metals caused almost the same inhibition to EhNvINV and EhCvINV. No statistically significant differences were observed between EhNvINV and EhCvINV in K m and k cat values for sucrose. The results provided evidence that the observed residue divergences had little influence on the enzyme properties of VIN in E. haichowensis, and the varied VIN activities between the contrasting populations under Cu stress were not relevant to the amino acid divergences in the proteins. Also, some other possible reasons accounting for this difference in invertase activities were discussed, such as up-regulation of expression of the EhCvINV gene under Cu stress, as Cu tolerance mechanisms in Cu-mine plants.

Rhizobium tibeticum activated with a mixture of flavonoids alleviates nickel toxicity in symbiosis with fenugreek (Trigonella foenum graecum L.)

The objective of this study is to explore the response of an activated Rhizobium tibeticum inoculum with a mixture of hesperetin (H) and apigenin (A) to improve the growth, nodulation, and nitrogen fixation of fenugreek (Trigonella foenum graecum L.) grown under nickel (Ni) stress. Three different sets of fenugreek seed treatments were conducted, in order to investigate the activated R. tibeticum pre-incubation effects on nodulation, nitrogen fixation and growth of fenugreek under Ni stress. Group (I): uninoculated seeds with R. tibeticum, group (II): inoculated seeds with uninduced R. tibeticum group (III): inoculated seeds with induced R. tibeticum. The present study revealed that Ni induced deleterious effects on rhizobial growth, nod gene expression, nodulation, phenylalanine ammonia-lyase (PAL) and glutamine synthetase activities, total flavonoids content and nitrogen fixation, while the inoculation with an activated R. tibeticum significantly improved these values compared with plants inoculated with uninduced R. tibeticum. PAL activity of roots plants inoculated with induced R. tibeticum and grown hydroponically at 75 and 100 mg L(-1) Ni and was significantly increased compared with plants receiving uninduced R. tibeticum. The total number and fresh mass of nodules, nitrogenase activity of plants inoculated with induced cells grown in soil treated up to 200 mg kg(-1) Ni were significantly increased compared with plants inoculated with uninduced cells. Plants inoculated with induced R. tibeticum dispalyed a significant increase in the dry mass compared with those treated with uninduced R. tibeticum. Activation of R. tibeticum inoculum with a mixture of hesperetin and apigenin has been proven to be practically important in enhancing nodule formation, nitrogen fixation and growth of fenugreek grown in Ni contaminated soils.