The study of orchid mycorrhizal interactions is particularly complex because of the peculiar life cycle of these plants and their diverse trophic strategies. Here, transcriptomics has been applied to ...investigate gene expression in the mycorrhizal roots of
, a terrestrial mixotrophic orchid that associates with ectomycorrhizal fungi in the genus
. Our results provide new insights into the mechanisms underlying plant-fungus interactions in adult orchids in nature and in particular into the plant responses to the mycorrhizal symbiont(s) in the roots of mixotrophic orchids. Our results indicate that amino acids may represent the main nitrogen source in mycorrhizal roots of
, as already suggested for orchid protocorms and other orchid species. The upregulation, in mycorrhizal
roots, of some symbiotic molecular marker genes identified in mycorrhizal roots from other orchids as well as in arbuscular mycorrhiza, may mirror a common core of plant genes involved in endomycorrhizal symbioses. Further efforts will be required to understand whether the specificities of orchid mycorrhiza depend on fine-tuned regulation of these common components, or whether specific additional genes are involved.
In the present study, the phytoremedation potential along with growth, physiological and biochemical response of tomato (Solanum lycopersicum) was assessed under heavy metal(loid) (HM) and arbuscular ...mycorrhizal fungus (AMF) amendment. Effect of AMF on uptake and accumulation of metal(loid)s was assessed and accumulation characteristics were expressed in terms of bioabsorption coefficient (BAC), bioconcentration factor (BCF), translocation factor (TLF) and transfer factor (TF). Results showed that AMF-inoculated plants showed not only a better growth, chlorophyll content, strengthened non-enzymatic and enzymatic defense mechanism, but also accumulated higher concentration of metal(loid)s. The correlation between biochemical and physiological parameters was significant at 0.01 level. A significant difference (p ≤ 0.001) in antioxidant enzyme activity was found on increasing metal(loid) dose and application of AMF. The accumulation of Cd and Pb in edible part exceeded the chronic reference dose stated by USEPA. The target hazard quotient (THQ) was >1 for Cd and Pb, whereas <1 for As. The study shows that tomato has good potential as Cd and Pb phytoremediator, hence must not be consumed when grown on Cd or Pb contaminated sites.
Arbuscular mycorrhizal fungi (AMF) are crucial for ecosystem functioning, and thus have potential use for sustainable agriculture. In this study, we investigated the impact of organic and mineral ...fertilizers on the AMF community composition and content of Glomalin-related soil protein (GRSP) in a field experimental station which was established in 1979, in the Loess Plateau of China. Roots and soils were sampled three times during the growing period of winter wheat in 2008. The treatments including: N (inorganic N), NP (inorganic N and P), SNP (straw, inorganic N and P), M (farmyard manure), MNP (farmyard manure, inorganic N and P), and CK (no fertilization). AMF communities of root and soil samples were analyzed using PCR-DGGE, cloning and sequencing techniques; and GRSP content was determined by Bradford assay. Our results indicated that spore density, GRSP, and AMF community varied significantly in soils of long-term fertilization plots at three different wheat growing stages. The effects of wheat growing period on AMF community in roots were much more evident than fertilization regimes. However, the diversity of AMF was low in our study field. Up to five AMF phylotypes appeared in each sample, with the overwhelming dominance of a Glomus-like phylotype affiliated to G. mosseae. GRSP content was correlated positively with organic carbon, total phosphorus, available phosphorus, soil pH, and spore densities, but correlated negatively with soil C/N (P<0.05). The results of our study highlight that the richness of AMF in Loess Plateau agricultural region is low, and long-term fertilization, especially amendments with manure and straw, has beneficial effects on accumulation of soil organic carbon, spore density, GRSP content, and AMF diversity. Host phenology, edaphic factors (influenced by long-term fertilization), and habitats interacted to affect the AMF community and agoecosystem functioning. Additionally, soil moisture and pH make a greater contribution than other determined soil parameters to the AMF community dynamics in such a special semi-arid agroecosystem where crops rely greatly on rainfall.
Root-associated endophytic fungi like Serendipita indica and arbuscular mycorrhizal (AM) fungi can improve plant growth and root construction, but the potential mechanism is unclear. In this study, ...Funneliformis mosseae (an AM fungus) and S. indica, singly or in combination were inoculated into trifoliate orange (Poncirus trifoliata) seedlings, to assess changes in biomass and root morphological traits, coupled with auxins and cytokinins concentrations in leaves and roots and the expression of auxin synthesis and transporter protein genes. After 20 weeks of inoculation with these fungi, shoot and root biomass, root total length, taproot length, average diameter, surface area, volume, and the number of lateral roots in 1st-, 2nd-, and 3rd-order were improved, and S. indica showed a relatively greater effect than F. mosseae and dual inoculation. Endophytic fungal inoculation also significantly increased the concentration of indoleacetic acid, indole butyric acid, trans-zeatin, dihydrozeatin, and isopentenyl adenine in leaves and roots, whilst F. mosseae and S. indica exhibited relatively greater effects on leaves and roots, respectively. Correlation analysis revealed that both biomass and root morphological traits (except root projected area) were significantly positively associated with endogenous auxins and cytokinins. In addition, the inoculated plants recorded comparatively higher expression levels of indoleacetic acid synthesis genes (PtTAA1, PtTAR2, PtYUC3, PtYUC4, PtYUC6, and PtYUC8) and indoleacetic acid transporter protein genes (PtAUX1, PtLAX1, PtLAX2, PtLAX3, PtPIN1, PtPIN3, PtPIN4, PtABCB1, and PtABCB19) than the non-inoculated plants, among which F. mosseae and S. indica showed better effects in leaves and roots, respectively. These results suggest that root-associated endophytic fungi improved plant growth and root architecture, which were associated with changes in endogenous auxins and cytokinins.
Strigolactones were originally identified as stimulators of the germination of root-parasitic weeds that pose a serious threat to resource-limited agriculture. They are mostly exuded from roots and ...function as signalling compounds in the initiation of arbuscular mycorrhizae, which are plant-fungus symbionts with a global effect on carbon and phosphate cycling. Recently, strigolactones were established to be phytohormones that regulate plant shoot architecture by inhibiting the outgrowth of axillary buds. Despite their importance, it is not known how strigolactones are transported. ATP-binding cassette (ABC) transporters, however, are known to have functions in phytohormone translocation. Here we show that the Petunia hybrida ABC transporter PDR1 has a key role in regulating the development of arbuscular mycorrhizae and axillary branches, by functioning as a cellular strigolactone exporter. P. hybrida pdr1 mutants are defective in strigolactone exudation from their roots, resulting in reduced symbiotic interactions. Above ground, pdr1 mutants have an enhanced branching phenotype, which is indicative of impaired strigolactone allocation. Overexpression of Petunia axillaris PDR1 in Arabidopsis thaliana results in increased tolerance to high concentrations of a synthetic strigolactone, consistent with increased export of strigolactones from the roots. PDR1 is the first known component in strigolactone transport, providing new opportunities for investigating and manipulating strigolactone-dependent processes.
Arbuscular mycorrhizal (AM) fungi play an essential role for the nutrient uptake of the majority of land plants, including many important crop species. The extraradical mycelium of the fungus takes ...up nutrients from the soil, transfers these nutrients to the intraradical mycelium within the host root, and exchanges the nutrients against carbon from the host across a specialized plant-fungal interface. The contribution of the AM symbiosis to the phosphate nutrition has long been known, but whether AM fungi contribute similarly to the nitrogen nutrition of their host is still controversially discussed. However, there is a growing body of evidence that demonstrates that AM fungi can actively transfer nitrogen to their host, and that the host plant with its carbon supply stimulates this transport, and that the periarbuscular membrane of the host is able to facilitate the active uptake of nitrogen from the mycorrhizal interface. In this review, our current knowledge about nitrogen transport through the fungal hyphae and across the mycorrhizal interface is summarized, and we discuss the regulation of these pathways and major research gaps.
Arbuscular mycorrhizas (AM) play an important role in plant P and Zn nutrition; however, relatively few studies have directly investigated the interactive effects of these nutrients on plants. ...Therefore, we undertook a glasshouse experiment to study the effects of Zn and P on AM formation and functioning. A mycorrhiza defective tomato mutant (
rmc
) and its mycorrhizal wild-type progenitor (76R) were used in this experiment. Plants were grown in soil amended with five Zn concentrations, ranging from deficient to toxic, and two levels of P addition. The addition of Zn and P to the soil over a range of concentrations had profound effects on plant growth and nutrition and mycorrhizal colonization. Mycorrhizal benefits were the greatest when plants were grown under low soil P and Zn. Furthermore, the effect of soil Zn supply on plant growth, nutrition, and AM colonization was strongly influenced by the concentration of P in the soil. Thus, studies of AM and Zn (or other nutrients of interest) should take into account the impact of soil P concentration on the role of AM in plant Zn acquisition, under both deficient and toxic soil Zn concentrations.
Phosphorus (P) is essential for productivity of alpine grassland ecosystems, which are sensitive to global warming. We tested the hypotheses that (1) mobilized ‘calcium‐bound inorganic P’ (Ca‐Pi) is ...a major source of plant‐available P in alpine meadows with alkaline soils after long‐term warming, (2) mobilization of Ca‐Pi is linked to effective plant carboxylate‐releasing P‐acquisition strategies under warming, and (3) the mobilization is also related to plant nitrogen (N)‐acquisition. We conducted an 8‐year warming experiment in an alpine meadow (4635 m above sea level) on the Qinghai‐Tibetan Plateau. A significant increase in P concentration in both aboveground and belowground biomass indicates an increased mobilization and assimilation of P by plants under warming. We observed a significant decrease in Ca‐Pi, no change in moderately‐labile organic P, and an increase in highly resistant organic P after warming. There was no increase in phosphatase activities. Our results indicate that Ca‐Pi, rather than organic P was the major source of plant‐available P for alpine meadows under warming. Higher leaf manganese concentrations of sedges and forbs after warming indicate that carboxylates released by these plants are a key mechanism of Ca‐Pi mobilization. The insignificant increase in Rhizobiales after warming and the very small cover of legumes show a minor role of N‐acquisition strategies in solubilizing phosphate. The insignificant change in relative abundance of mycorrhizal fungi and bacteria related to P cycling after warming shows a small contribution of microorganisms to Ca‐Pi mobilization. The significant increase in leaf N and P concentrations and N:P ratio of grasses and no change in sedge leaf N:P ratio reflect distinct responses of plant nutrient status to warming due to differences in P‐acquisition strategies. We highlight the important effects of belowground P‐acquisition strategies, especially plant carboxylate‐releasing P‐acquisition strategies on responses of plants to global changes in alpine meadows.
Phosphorus (P) is essential for productivity of alpine grassland ecosystems, which are sensitive to global warming. The soil Calcium‐bound inorganic phosphorus (Ca‐Pi) significantly decreased and moderately‐labile organic P showed no change, while highly‐resistant organic P increased under an 8 year of warming in an alpine meadow on the Qinghai‐Tibet Plateau. Carboxylates released by sedge and forbs, indicated by the high leaf manganese concentrations, accelerated the Ca‐Pi mobilization, to meet the plant P demand under warming climate. Belowground P‐acquisition strategies, especially plant carboxylate‐releasing P‐acquisition strategies influence responses of plants to global changes in alpine meadows.
Plants and arbuscular mycorrhizal fungi (AMF) mutualistic interactions are essential for sustainable agriculture production. Although it is shown that AMF inoculation improves cassava physiological ...performances and yield traits, the molecular mechanisms involved in AM symbiosis remain largely unknown. Herein, we integrated metabolomics and transcriptomics analyses of symbiotic (Ri) and asymbiotic (CK) cassava roots and explored AM-induced biochemical and transcriptional changes.
Three weeks (3w) after AMF inoculations, proliferating fungal hyphae were observable, and plant height and root length were significantly increased. In total, we identified 1,016 metabolites, of which 25 were differentially accumulated (DAMs) at 3w. The most highly induced metabolites were 5-aminolevulinic acid, L-glutamic acid, and lysoPC 18:2. Transcriptome analysis identified 693 and 6,481 differentially expressed genes (DEGs) in the comparison between CK (3w) against Ri at 3w and 6w, respectively. Functional enrichment analyses of DAMs and DEGs unveiled transport, amino acids and sugar metabolisms, biosynthesis of secondary metabolites, plant hormone signal transduction, phenylpropanoid biosynthesis, and plant-pathogen interactions as the most differentially regulated pathways. Potential candidate genes, including nitrogen and phosphate transporters, transcription factors, phytohormone, sugar metabolism-related, and SYM (symbiosis) signaling pathway-related, were identified for future functional studies.
Our results provide molecular insights into AM symbiosis and valuable resources for improving cassava production.
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