Combining the Anticancer and Immunomodulatory Effects of Astragalus and Shiitake as an Integrated Therapeutic Approach.

Astragalus root (Huang Qi) and Shiitake mushrooms (Lentinus edodes) are both considered medicinal foods and are frequently used in traditional Chinese medicine due to their anticancer and immunomodulating properties. Here, the scientific literatures describing evidence for the anticancer and immunogenic properties of Shiitake and Astragalus were reviewed. Based on our experimental data, the potential to develop medicinal food with combined bioactivities was assessed using Shiitake mushrooms grown over Astragalus beds in a proprietary manufacturing process, as a novel cancer prevention approach. Notably, our data suggest that this new manufacturing process can result in transfer and increased bioavailability of Astragalus polysaccharides with therapeutic potential into edible Shiitake. Further research efforts are required to validate the therapeutic potential of this new Hengshan Astragalus Shiitake medicinal food.

Flower and pod development, grain-setting characteristics and grain yield in Chinese milk vetch (Astragalus sinicus L.) in response to pre-anthesis foliar application of paclobutrazol.

The number of grains per unit land area is the most important grain yield component in Chinese milk vetch. Flower and pod survival seem to be critical determinants of grain number, which is related to the number of fertile flowers and pods during the anthesis period. Flower and pod growth are frequently considered the key determinants to establish grain number. The objective of this study was to explore the influences of paclobutrazol on flower and pod development, grain-setting characteristics and grain yield in Chinese milk vetch under different concentrations of foliar spray and try to explore the physiological regulatory mechanisms. Field experiments were carried out during the 2017-2018 and 2018-2019 growing seasons at the Dayuzhuang experimental field. The experiment involved the Chinese milk vetch cultivar "Xinzi No. 1" and six levels of foliar application of paclobutrazol, 0, 200, 300, 400, 500, and 600 mg L-1, in treatments CK, T1, T2, T3, T4, and T5, respectively. Foliar spray was applied once, at the squaring stage. In comparison with the CK treatment, all of the paclobutrazol treatments yielded, to various degrees, increased values of the number of inflorescences per unit area, number of pods per unit area, grain-setting rate of pods, and number of grains per pod in all six inflorescence layers, with the largest increases observed in the T3 treatment. In the T3 treatment compared with the CK treatment, from the first to sixth inflorescence layers, the number of inflorescences per unit area was increased by 34.07-58.97%, the number of pods per unit area was increased by 39.69-68.35%, the grain number per pod was increased by 44.31-53.69%, and the grain-setting rate of pods was increased by 1.84-4.89%. An analysis of yield composition revealed that the paclobutrazol spray treatment had little impact on the grain weight of Chinese milk vetch. The correlations between the concentration of paclobutrazol spray and the grain yield of Chinese milk vetch reached a significant level. Grain yield was highest at the paclobutrazol concentration of 373.10 mg/L. The inflorescence contents of gibberellic acid 3 (GA3), indole-3-acetic acid (IAA), and abscisic acid (ABA) were reduced, whereas that of cytokinin (CTK) was increased, by foliar application of paclobutrazol (400 mg L-1, T3 treatment) relative to CK treatment during the stages of flowers and pods developing into grains.

Nitrogen Fertilizer Levels Affect the Growth and Quality Parameters of Astragalus mongolica.

Owing to overexploitation, wild resources of Astragalus mongolica, a Chinese herbal plant that is widely distributed in the arid and semi-arid areas of Northern China, have gradually become exhausted, and therefore, commercial cultivation is increasingly important to meet the growing demand for astragalus and reduce the pressure on wild populations. Nitrogen level is an important factor that affects the yield and quality of A. mongolica. However, uniform standards for fertilization among production areas have not yet been determined. In this study, the effect of nitrogen fertilizer treatment on the yield and quality of A. mongolica in the Qinghai-Tibet Plateau was explored using a control treatment (no added nitrogen, N0) and five different nutrient levels: 37.5 kg/ha (N1), 75 kg/ha (N2), 112.5 kg/ha (N3), 150 kg/ha (N4), and 187.5 kg/ha (N5). According to grey relational analysis, the optimal nitrogen fertilizer treatment was the N4 level followed by the N5 and N2 levels. Nitrogen fertilizer significantly increased the root biomass, plant height, root length, and root diameter. However, nitrogen fertilization had no significant effect on the content of Astragaloside IV and mullein isoflavone glucoside. The content of ononin and calycosin continually accumulated throughout the growing period. The results showed that the ononin and calycosin content under N4 and N2 is higher than other levels and there is not significantly different between different nitrogen fertilizer levels about them. The content of formononetin decreased gradually with the progression of the growing season. The optimal nitrogen fertilizer treatment for A. mongolica is recommended to be 150 kg/ha and the content of active compounds and yield were observed to reach the maximum in October.

De novo transcriptome characterisation of two auxin-related genes associated with plant growth habit in Astragalus adsurgens Pall.

Astragalus adsurgens Pall., a perennial legume native to China, is commonly used as a forage crop. And it has great value for sustainable development of grasslands in arid and semi arid regions. However, to date, little is known regarding the A. adsurgens genome, and no studies have determined whether it would be possible to improve the germplasm of A. adsurgens through genetic modification. In this study, we used an RNA-seq protocol to generate a de novo transcriptome including 151,516 unigenes of A. adsurgens. We compared the transcriptomes of A. adsurgens having different growth habits (prostrate/erect) and identified 14,133 single nucleotide polymorphism sites (SNP) in 8,139 unigenes. Differential expression gene (DEG) analysis suggested that 10,982 unigenes were up-regulated in the prostrate plant relative to the erect plant, while 10,607 unigenes were down-regulated. Of the 21,589 DEG, Unigene72782_All (LAX4) and CL12494.Contig3_All (TIR1), an auxin transporter gene and an auxin transport inhibitor gene, respectively, were predicted to influence the growth habit of A. adsurgens, which were verified by qRT-PCR in these phenotypes. These results suggest that auxin transport was more active in the prostrate plant than in the erect plant, resulting in asymmetric distribution of auxin that affects the growth habit of A. adsurgens. Overall, this study may provide a basis for future research on key genes in A. adsurgens and may deepen our understanding of the molecular mechanisms regulating plant growth habit.

[Effects of Chinese milk vetch intercropped with rape under straw mulching on soil aggregate and organic carbon character]. / 秸秆覆盖条件下紫云英间作油菜的土壤团聚体及有机碳特征.

There are severe soil erosion, shallow soil, reduction of soil organic matter, and poor soil and water conservation in purple soil areas in Southwest China, which become the main limiting factors for the sustainable development of agriculture. A series of buckets and field experiments in the field were employed to explore the soil aggregate and soil organic carbon in response to Chinese milk vetch intercropped with rape under straw mulching, aiming to improve soil aggregate structure and increase organic carbon content. Results showed that intercropped Chinese milk vetch increased soil micro-aggregate content in rape rhizosphere, and reduced soil aggregate mean mass diameter. The change of soil macro-aggregate in rape rhizosphere was mainly caused by the change of content of soil aggregate on 10-5 mm and 5-2 mm, while the soil micro-aggregate was mainly caused by soil aggregate on 0.25-0.053 mm. Intercropped Chinese milk vetch and straw mulching significantly increased soil organic carbon content after corn growing season, with increasing the content of soil organic carbon on 10-20 cm and 20-30 cm. Though intercropped Chinese milk vetch and straw mulching had less effect on soil total organic carbon in rape season, more and more significant effect on 0-10 cm, 10-20 cm, and 20-30 cm with rape growing, especially in stem elongation stage, flowering stage, and harvest stage. Our results showed that the characteristic of soil aggregate in rape rhizosphere could be changed by intercropped Chinese milk vetch, and that the content of soil organic carbon could be increased by Chinese milk vetch intercropped with rape under straw mul-ching.

How can a rare protected plant cope with the metal and metalloid soil pollution resulting from past industrial activities? Phytometabolites, antioxidant activities and root symbiosis involved in the metal tolerance of Astragalus tragacantha.

Astragalus tragacantha is a protected plant species in France that grows even in the trace metal and metalloid (TMM) polluted soils of the Calanques National Park (PNCal). Soils are mainly contaminated by lead, copper, zinc and arsenic. An ex situ experiment was conducted, firstly to determine the molecular responses and root traits involved in the TMM tolerance of this plant species by growing individuals in a soil from the surroundings of one of the brownfields of the PNCal, known as l'Escalette, where this plant species grows spontaneously. Secondly, in order to determine the plasticity of these responses, seeds were collected from three different populations, at l'Escalette (polluted site), one from the Frioul archipelago (non-polluted, insular site) and one from La Seyne (non-polluted, littoral site). The results of this study confirmed the capacity of A. tragacantha to germinate and grow in TMM contaminated soils. Only moderate significant variations in chlorophyll and flavonol indices, proline content and antioxidant activities were detected between polluted and control soil conditions for all populations. The main driver for A. tragacantha TMM tolerance seemed to be its ability to be associated with root symbionts i.e. arbuscular mycorrhizal fungi and dark septate endophytes, corresponding to a nutrient-uptake strategy trait. This work provides support for the challenge of A. tragacantha conservation along the littoral of the PNCal, because increasing the number of A. tragacantha individuals would both increase vegetation cover of the polluted soils to reduce the pollution transfer and reinforce the populations of this species.

Effects of Elevated CO2 on the Swainsonine Chemotypes of Astragalus lentiginosus and Astragalus mollissimus.

Rapid changes in the Earth's atmosphere and climate associated with human activity can have significant impacts on agriculture including livestock production. CO2 concentration has risen from the industrial revolution to the current time, and is expected to continue to rise. Climatic changes alter physiological processes, growth, and development in numerous plant species, potentially changing concentrations of plant secondary compounds. These physiological changes may influence plant population density, growth, fitness, and toxin concentrations and thus influence the risk of toxic plants to grazing livestock. Locoweeds, swainsonine-containing Astragalus species, are one group of plants that may be influenced by climate change. We evaluated how two different swainsonine-containing Astragalus species responded to elevated CO2 concentrations. Measurements of biomass, crude protein, water soluble carbohydrates and swainsonine concentrations were measured in two chemotypes (positive and negative for swainsonine) of each species after growth at CO2 levels near present day and at projected future concentrations. Biomass and water soluble carbohydrate concentrations responded positively while crude protein concentrations responded negatively to elevated CO2 in the two species. Swainsonine concentrations were not strongly affected by elevated CO2 in the two species. In the different chemotypes, biomass responded negatively and crude protein concentrations responded positively in the swainsonine-positive plants compared to the swainsonine-negative plants. Ultimately, changes in CO2 and endophyte status will likely alter multiple physiological responses in toxic plants such as locoweed, but it is difficult to predict how these changes will impact plant herbivore interactions.

A swainsonine survey of North American Astragalus and Oxytropis taxa implicated as locoweeds.

Swainsonine, an indolizidine alkaloid with significant physiological activity, is an α-mannosidase and mannosidase II inhibitor that causes lysosomal storage disease and alters glycoprotein processing. Swainsonine is found in a number of plant species worldwide, and causes severe toxicosis in livestock grazing these plants, leading to a chronic wasting disease characterized by weight loss, depression, altered behavior, decreased libido, infertility, and death. Swainsonine has been detected in 19 Astragalus and 2 Oxytropis species in North America by thin layer chromatography, gas chromatography-mass spectrometry, liquid chromatography-mass spectrometry and a jack bean α-mannosidase inhibition assay. In addition, 5 species in North America are presumed to contain swainsonine based upon reports from field cases. Many of these plant species have not been analyzed for swainsonine using modern instrumentation such as gas or liquid chromatography coupled with mass spectrometry. To provide clarification, 22 Astragalus species representing 93 taxa and 4 Oxytropis species representing 18 taxa were screened for swainsonine using both liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry. Swainsonine was detected in 48 Astragalus taxa representing 13 species and 5 Oxytropis taxa representing 4 species. Forty of the fifty-three swainsonine-positive taxa had not been determined to contain swainsonine previously using liquid or gas chromatography coupled with mass spectrometry. The list of swainsonine-containing taxa reported here will serve as a reference for risk assessment and diagnostic purposes.

Effect of vegetation rehabilitation on soil carbon and its fractions in Mu Us Desert, northwest China.

Although vegetation rehabilitation on semi-arid and arid regions may enhance soil carbon sequestration, its effects on soil carbon fractions remain uncertain. We carried out a study after planting Artemisia ordosica (AO, 17 years), Astragalus mongolicum (AM, 5 years), and Salix psammophila (SP, 16 years) on shifting sand land (SL) in the Mu Us Desert, northwest China. We measured total soil carbon (TSC) and its components, soil inorganic carbon (SIC) and soil organic carbon (SOC), as well as the light and heavy fractions within soil organic carbon (LF-SOC and HF-SOC), under the SL and shrublands at depths of 100 cm. TSC stock under SL was 27.6 Mg ha(-1), and vegetation rehabilitation remarkably elevated it by 40.6 Mgha(-1), 4.5 Mgha(-1), and 14.1 Mgha(-1) under AO, AM and SP land, respectively. Among the newly formed TSC under the three shrublands, SIC, LF-SOC and HF-SOC accounted for 75.0%, 10.7% and 13.1% for AO, respectively; they made up 37.0%, 50.7% and 10.6% for AM, respectively; they occupied 68.6%, 18.8% and 10.0% for SP, respectively. The accumulation rates of TSC within 0-100 cm reached 238.6 g m(-2) y(-1), 89.9 g m(-2) y(-1) and 87.9 g m(-2) y(-1) under AO, AM and SP land, respectively. The present study proved that the accumulation of SIC considerably contributed to soil carbon sequestration, and vegetation rehabilitation on shifting sand land has a great potential for soil carbon sequestration.

[Influence of Different Growing Years on Accumulation of Flavonoids and Saponins in Astragali Radix].

OBJECTIVE: To study the effects of different growing years on the accumulation of flavonoids and saponins in Astragali Radix, in order to offer evidence to determine the most appropriate harvest time. METHODS: HPLC method was developed for the determination of the contents of flavonoids and saponins. RESULTS: The contents of flavonoids and saponins in different growing years of Astragali Radix existed obvious differences, the longer growing, the content was relatively higher. CONCLUSION: With the increase of growing years, the contents of flavonoids and saponins are roughly rising year by year, the harvest time has a great influence on the accumulation of the compositions.

Responses of social and solitary bees to pulsed floral resources.

Pulsed food resources lead to mismatches between distribution of consumers and resources in space and time. Many studies have investigated how pollinators and floral resources covary in space, but few have looked at their covariance among years. I studied responses of two bee taxa, Bombus (a social genus) and Anthophora (a solitary genus), to variation in flowering by Astragalus scaphoides, a perennial herb that flowers in alternate years. First, I quantified the rate at which individual plants were visited by bees. Anthophora showed evidence of a demographic response to resource pulses--that is, more individuals were seen in the year after a high-flowering year--whereas Bombus did not. Second, I quantified pollinator behavior by following individual bees and recording the proportion of visits to A. scaphoides within single foraging bouts. The proportion of visits to A. scaphoides by both taxa increased with A. scaphoides's flowering density. Higher specialization in high-flowering years likely makes both taxa better pollinators in high-flowering years. If these taxa differ in effectiveness as pollinators, then these responses translate into variation in pollination services in space and time, specifically, more activity by Bombus in high-flowering years and more by Anthophora in years following high-flowering years. They also emphasize that pollinator activity depends in part on past-as well as current-floral resources.

Inoculation of Astragalus racemosus and Astragalus convallarius with selenium-hyperaccumulator rhizosphere fungi affects growth and selenium accumulation.

Little is known about how fungi affect plant selenium (Se) accumulation. Here we investigate the effects of two fungi on Se accumulation, translocation, and chemical speciation in the hyperaccumulator Astragalus racemosus and the non-accumulator Astragalus convallarius. The fungi, Alternaria astragali (A3) and Fusarium acuminatum (F30), were previously isolated from Astragalus hyperaccumulator rhizosphere. A3-inoculation enhanced growth of A. racemosus yet inhibited growth of A. convallarius. Selenium treatment negated these effects. F30 reduced shoot-to-root Se translocation in A. racemosus. X-ray microprobe analysis showed no differences in Se speciation between inoculation groups. The Astragalus species differed in Se localization and speciation. A. racemosus root-Se was distributed throughout the taproot and lateral root and was 90 % organic in the lateral root. The related element sulfur (S) was present as a mixture of organic and inorganic forms in the hyperaccumulator. Astragalus convallarius root-Se was concentrated in the extreme periphery of the taproot. In the lateral root, Se was exclusively in the vascular core and was only 49 % organic. These findings indicate differences in Se assimilation between the two species and differences between Se and S speciation in the hyperaccumulator. The finding that fungi can affect translocation may have applications in phytoremediation and biofortification.

[Status and analysis of Astragali Radix resource in China].

To explore the status of the resources of Astragali Radix, a survey on its germplasm resources was carried out. Some conclusions can be drawn for Astragali Radix: the major source is the cultivated Astragalus mongolicus. The new major cultivation areas for A. mongolicus and A. membranaceus are Shandong and Gansu province. The semi-wildly planting model in Shanxi province maintains the genuine trait of Astragali Radix, but its yield is limited, and now a combination model has been developed. The major problems for Astragali Radix are the selection of planting sites, the rot root and difficulty in collecting and processing. Several developmental proposals for Astragali Radix were put forward including rational distribution of planting areas, establishment of standard system, development and standardization of producing technologies.

Selenium hyperaccumulation by Astragalus (Fabaceae) does not inhibit root nodule symbiosis.

PREMISE OF STUDY: A survey of the root-nodule symbiosis in Astragalus and its interaction with selenium (Se) has not been conducted before. Such studies can provide insight into how edaphic conditions modify symbiotic interactions and influence partner coevolution. In this paper plant-organ Se concentration ([Se]) was investigated to assess potential Se exposure to endophytes. • METHODS: Selenium distribution and molecular speciation of root nodules from Se-hyperaccumulators Astragalus bisulcatus, A. praelongus, and A. racemosus was determined by Se K-edge x-ray absorption spectroscopy. A series of greenhouse experiments were conducted to characterize the response of root-nodule symbiosis in Se-hyperaccumulators and nonhyperaccumulators. • KEY RESULTS: Nodules in three Se-hyperaccumulators (Astragalus crotalariae, A. praelongus, and A. preussii) are reported for the first time. Leaves, flowers, and fruits from Se-hyperaccumulators were routinely above the hyperaccumulator threshold (1,000 µg Se g(-1) DW), but root samples rarely contained that amount, and nodules never exceeded 110 µg Se g(-1) DW. Nodules from A. bisulcatus, A. praelongus, and A. racemosus had Se throughout, with a majority stored in C-Se-C form. Finally, an evaluation of nodulation in Se-hyperaccumulators and nonhyperaccumulators indicated that there was no nodulation inhibition because of plant Se tolerance. Rather, we found that in Se-hyperaccumulators higher levels of Se treatment (up to 100 µM Se) corresponded with higher nodule counts, indicating a potential role for dinitrogen fixation in Se-hyperaccumulation. The effect was not found in nonhyperaccumulators. • CONCLUSIONS: As the evolution of Se hyperaccumulation in Astragalus developed, root-nodule symbiosis may have played an integral role.

Identification and characterization of selenate- and selenite-responsive genes in a Se-hyperaccumulator Astragalus racemosus.

Plants with capacity to accumulate high levels of selenium (Se) are desired for phytoremediation and biofortification. Plants of genus Astragalus accumulate and tolerate high levels of Se, but their slow growth, low biomass and non-edible properties limit their direct utilization. Genetic engineering may be an alternative way to produce edible or high biomass Se-accumulating plants. The first step towards this goal is to isolate genes that are responsible for Se accumulation and tolerance. Later, these genes can be introduced into other edible and high biomass plants. In the present study, we applied fluorescent differential display to analyze the transcript profile of Se-hyperaccumulator A. racemosus treated with 20 µM selenate (K(2)SeO(4)) for 2 weeks. Among 125 identified Se-responsive candidate genes, the expression levels of nine were induced or suppressed more than twofold by selenate treatment in two independent experiments while 14 showed such changes when treated with selenite (K(2)SeO(3)). Six of them were found to respond to both selenate and selenite treatments. A novel gene CEJ367 was found to be highly induced by both selenate (1,920-fold) and selenite (579-fold). Root- or shoot-preferential expression of nine genes was further investigated. These identified genes may allow us to create Se-enriched transgenic plants.

Are dormant plants hedging their bets? Demographic consequences of prolonged dormancy in variable environments.

During the growing season, some individuals in perennial plant populations may remain alive belowground while others emerge. This phenomenon, known as prolonged dormancy, seems maladaptive, because prolonged dormancy delays growth and reproduction. However, prolonged dormancy may offer the benefit of safety while belowground, leading to the hypothesis that prolonged dormancy is a bet-hedging strategy. We evaluated this hypothesis using a 25-year demographic study of Astragalus scaphoides, an iteroparous perennial plant. First, we determined the relationship between prolonged dormancy and fitness using data from individuals in our population. This analysis showed that prolonged dormancy decreased arithmetic mean fitness and reduced variance in fitness. Geometric mean fitness was maximized at intermediate levels of prolonged dormancy. Empirical patterns of lifetime reproductive success confirm this relationship. We also compared fitness of plants in our population to hypothetical plants without prolonged dormancy, which generally revealed benefits of prolonged dormancy, even if plants could forgo prolonged dormancy without costs to other vital rates. Therefore, prolonged dormancy may indeed function as a bet-hedging strategy, but the benefits of remaining belowground outweigh the costs only for a subset of individuals. Bet hedging has been demonstrated in plants with simple life histories, such as annuals and monocarpic perennials; we present evidence that bet hedging may be important for plants with more complex life histories.

Interactions of selenium hyperaccumulators and nonaccumulators during cocultivation on seleniferous or nonseleniferous soil--the importance of having good neighbors.

• This study investigated how selenium (Se) affects relationships between Se hyperaccumulator and nonaccumulator species, particularly how plants influence their neighbors' Se accumulation and growth. • Hyperaccumulators Astragalus bisulcatus and Stanleya pinnata and nonaccumulators Astragalus drummondii and Stanleya elata were cocultivated on seleniferous or nonseleniferous soil, or on gravel supplied with different selenate concentrations. The plants were analyzed for growth, Se accumulation and Se speciation. Also, root exudates were analyzed for Se concentration. • The hyperaccumulators showed 2.5-fold better growth on seleniferous than on nonseleniferous soil, and up to fourfold better growth with increasing Se supply; the nonaccumulators showed the opposite results. Both hyperaccumulators and nonaccumulators could affect growth (up to threefold) and Se accumulation (up to sixfold) of neighboring plants. Nonaccumulators S. elata and A. drummondii accumulated predominantly (88-95%) organic C-Se-C; the remainder was selenate. S. elata accumulated relatively more C-Se-C and less selenate when growing adjacent to S. pinnata. Both hyperaccumulators released selenocompounds from their roots. A. bisulcatus exudate contained predominantly C-Se-C compounds; no speciation data could be obtained for S. pinnata. • Thus, plants can affect Se accumulation in neighbors, and soil Se affects competition and facilitation between plants. This helps to explain why hyperaccumulators are found predominantly on seleniferous soils.

Floral ontogeny in Astragalus compactus (Leguminosae: Papilionoideae: Galegeae): variable occurrence of bracteoles and variable patterns of sepal initiation.

Comparative studies of floral ontogeny represent a growing field that promise to provide new insights on floral evolution. Floral ontogenetic information has been used successfully in Leguminosae for re-examining phylogenetic relationships at different levels. Using epi-illumination light microscopy, we present original ontogenetic data in Astragalus compactus, which was chosen because of its unusual arrangement of inflorescence and variable occurrence of bracteoles on flowers. Based on our results, uncommon ontogeny of the inflorescence led to the arrangement of flowers in four different positions. Variation was observed not only in the presence of bracteoles, but also in the order of sepal initiation in flowers of the same inflorescence. Surprisingly, besides the widely stated unidirectional pattern, bidirectional, sequential and an atypical unreported order were observed. High degree of overlapping between whorls and formation of two types of common primordia also were found. The variable occurrence of bracteoles suggests that the species is in an intermediate state towards fully lacking of bracteoles. We propose that the variability of the sequence of sepal initiation is possibly a consequence of the function of mechanical forces generated by surrounding leaves. Relationships between mechanical force and auxin signalling are discussed.

Ecological aspects of plant selenium hyperaccumulation.

Hyperaccumulators are plants that accumulate toxic elements to extraordinary levels. Selenium (Se) hyperaccumulators can contain 0.1-1.5% of their dry weight as Se, levels toxic to most other organisms. In this review we summarise what is known about the ecological functions and implications of Se (hyper)accumulation by plants. Selenium promotes hyperaccumulator growth and also offers a plant several ecological advantages through negative effects on Se-sensitive partners. High tissue Se levels reduce herbivory and pathogen infection, and high-Se litter deposition can inhibit neighbouring plants. There is no evidence for a cost of hyperaccumulation in terms of reproductive functions or pollinator visitation. Hyperaccumulators offer a niche for Se-tolerant herbivores, pollinators, microbes and neighbouring plants. They may even facilitate these partners through Se enrichment: neighbouring plants with elevated Se levels enjoy enhanced growth and reduced herbivory. Through combined negative and positive effects on ecological partners, Se hyperaccumulators likely affect local plant, microbial and animal species composition and richness, favouring Se-tolerant species at different trophic levels. By locally concentrating Se and altering its chemical form, Se hyperaccumulators likely play an important role in Se entry into, and Se cycling through, seleniferous ecosystems. These findings are of significance since they provide insight into the ecological reverberations of Se hyperaccumulation, and shed light on the possible selection pressures that have led to the evolution of this fascinating phenomenon. Better ecological insight will also help in the management of seleniferous areas and the agricultural production of Se-rich crops for phytoremediation or biofortification.

Identification of a novel gene for biosynthesis of a bacteroid-specific electron carrier menaquinone.

Ubiquinone (UQ) has been considered as an electron mediator in electron transfer that generates ATP in Rhizobium under both free-living and symbiosis conditions. When mutated, the dmtH gene has a symbiotic phenotype of forming ineffective nodules on Astragalus sinicus. The gene was isolated from a Mesorhizobium huakuii 7653R transposon-inserted mutant library. The DNA sequence and conserved protein domain analyses revealed that dmtH encodes demethylmenaquinone (DMK) methyltransferase, which catalyzes the terminal step of menaquinone (MK) biosynthesis. Comparative analysis indicated that dmtH homologs were present in only a few Rhizobia. Real-time quantitative PCR showed dmtH is a bacteroid-specific gene. The highest expression was seen at 25 days after inoculation of strain 7653R. Gene disruption and complementation tests demonstrated that the dmtH gene was essential for bacteroid development and symbiotic nitrogen fixation ability. MK and UQ were extracted from the wild type strain 7653R and mutant strain HK116. MK-7 was accumulated under microaerobic condition and UQ-10 was accumulated under aerobic condition in M. huakuii 7653R. The predicted function of DmtH protein was confirmed by the measurement of methyltransferase activity in vitro. These results revealed that MK-7 was used as an electron carrier instead of UQ in M. huakuii 7653R bacteroids.