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Plants colonized by arbuscular mycorrhizal (AM) fungi take up phosphate (Pi)via the mycorrhizal and the direct Pi uptake pathway. Our understanding of the molecular mechanisms involved in the regulation of these pathways is just emerging.Here, we have analyzed the molecular physiology of mycorrhizal Pi uptake in the tomato (Solanum lycopersicum) variety Micro-Tom and integrated the data obtained with studies on chemical signaling in mycorrhiza-inducible Pi transporter gene regulation.At high plant phosphorus (P) status, the mycorrhizal Pi uptake pathway was almost completely repressed and the mycorrhiza-inducible Pi transporter genes were down-regulated. A high plant P status also suppressed the activation of the mycorrhiza-specific StPT3 promoter fragment by phospholipid extracts containing the mycorrhiza signal lysophosphatidylcholine.Our results suggest that the mycorrhizal Pi uptake pathway is controlled at least partially by the plant host. This control involves components in common

Uptake of metals from uranium-rich phosphate rock was studied in Medicago truncatula plants grown in symbiosis with the arbuscular mycorrhizal fungus Glomus intraradices or in the absence of mycorrhizas. Shoot concentrations of uranium and thorium were lower in mycorrhizal than in non-mycorrhizal plants and root-to-shoot ratio of most metals was increased by mycorrhizas. This protective role of mycorrhizas was observed even at very high supplies of phosphate rock. In contrast, phosphorus uptake was similar at all levels of phosphate rock, suggesting that the P was unavailable to the plant-fungus uptake systems. The results support the role of arbuscular mycorrhiza as being an important component in phytostabilization of uranium. This is the first study to report on mycorrhizal effect and the uptake and root-to-shoot transfer of thorium from phosphate rock.

Phosphate sensors were developed by embedding fluorescent reporter proteins (FLIPPi) in polyacrylamide nanoparticles with diameters from 40 to 120 nm. The sensor activity and protein loading efficiency varied according to nanoparticle composition, that is, the total monomer content (% T) and the cross-linker content (% C). Nanoparticles with 28% T and 20% C were considered optimal as a result of relatively high loading efficiency (50.6%) as well as high protein activity (50%). The experimental results prove that the cross-linked polyacrylamide matrix could protect FLIPPi from degradation by soluble proteases to some extent. This nanoparticle embedding method provides a novel promising tool for in vivo metabolite studies. It also demonstrates a universal method for embedding different fragile bioactive elements, such as antibodies, genes, enzymes, and other functional proteins, in nanoparticles for, for example, sensing, biological catalysis, and gene delivery.

Genetically-encoded fluorescence resonance energy transfer (FRET) sensors for phosphate (P(i)) (FLIPPi) were engineered by fusing a predicted Synechococcus phosphate-binding protein (PiBP) to eCFP and Venus. Purified fluorescent indicator protein for inorganic phosphate (FLIPPi), in which the fluorophores are attached to the same PiBP lobe, shows P(i)-dependent increases in FRET efficiency. FLIPPi affinity mutants cover P(i) changes over eight orders of magnitude. COS-7 cells co-expressing a low-affinity FLIPPi and a Na(+)/P(i) co-transporter exhibited FRET changes when perfused with 100 microM P(i), demonstrating concentrative P(i) uptake by PiT2. FLIPPi sensors are suitable for real-time monitoring of P(i) metabolism in living cells, providing a new tool for fluxomics, analysis of pathophysiology or changes of P(i) during cell migration.

A Lycopersicon esculentum mutant (rmc) is resistant to colonization by most arbuscular mycorrhizal fungi (AMF), but one Glomus intraradices isolate (WFVAM 23) develops arbuscules and vesicles in the rmc cortex. It is unknown whether the symbiotic phosphate (Pi)-uptake pathway is operational in this interaction. Hyphal uptake of (32)Pi and expression of plant Pi transporter genes were investigated in the rmc mutant and its wild-type progenitor (76R) associated with three AMF. Hyphae transferred (32)Pi in all symbioses with 76R and in the rmc-G. intraradices WFVAM 23 symbiosis. The other AMF did not colonize rmc. The Pi transporter-encoding LePT1 and LePT2 were expressed constitutively or in P-starved roots, respectively. The mycorrhiza-inducible Pi transporters LePT3 and LePT4 were expressed only in plants with AMF colonization and symbiotic (32)Pi transfer. LePT3 and LePT4 transcripts were reliable markers for a functional mycorrhizal uptake pathway in rmc. Our novel approach to the physiology and molecular biology of P transport can be applied to other arbuscular-mycorrhizal symbioses, irrespective of the size of plant responses.

This study of functional diversity considers symbiotic associations between two plant species, Medicago truncatula and Lycopersicon esculentum, and seven species of arbuscular mycorrhizal fungi (AMF). The objective was to integrate physiological analyses with molecular techniques to test whether functional diversity between AMF species is not only apparent at the level of mycorrhiza formation, plant nutrient uptake and plant growth, but also at the molecular level as observed by variation in the root expression of plant genes involved in the plant's P-starvation response. The seven species of AMF varied widely in their influence on the root expression of MtPT2 and Mt4 from M. truncatula and LePT1 and TPSI1 from L. esculentum. At one extreme was Glomus mosseae, whereby its colonization of M. truncatula resulted in the greatest reduction in MtPT2 and Mt4 gene expression and the highest level of P uptake and growth, while at the other extreme was Gigaspora rosea, whereby colonization resulted in the highest levels of MtPT2 and Mt4 gene expression and the lowest P uptake and growth. The expression of LePT1 and TPSI1 within the roots of L. esculentum was low and relatively uniform across the seven mycorrhizas, reflecting the ability of this cultivar to maintain low and constant shoot P levels despite root colonization by a broad selection of AMF. This study extends current understanding of functional diversity and shows that plants can respond differently to AMF, not only at the level of colonization, nutrient uptake and growth, but also at the level of gene expression.

Abstract Biochar (BC) application to soil can potentially replace mineral P fertilizers and its effectiveness as fertilizer can be improved by plant inoculation with the phosphate-solubilizing microorganism Penicillium aculeatum (Pa). Arbuscular mycorrhiza (AM) fungi are important in plant P nutrition and may possibly act synergistically with Pa to improve the uptake of BC-P. Responses in wheat to inoculation with Pa and the AM fungus Rhizophagus irregularis were studied in a pot experiment at two levels of BC fertilization. Pots contained a mesh-enclosed, root free compartment with 33P-labelled soil for assessment of the AM contribution to P uptake and for studying if Pa would affect P uptake by the AM fungal hyphae. AM application suppressed wheat growth, albeit AM pathway had a major role in total P uptake at the two lowest P levels (nil or 20 mg BC-P kg−1 soil). Moreover, AM contribution had similar magnitudes in the presence and absence of Pa. Rhizosphere and bulk soil were actively colonized by Pa, both in the presence and absence of AM. The application of Pa or BC at a low rate increased AM-colonized root lengths. Although this was not translated to increased P uptake by wheat, the results suggest that AM and Pa can be combined without showing antagonistic interactions. However, more work is needed to understand how AM and Pa can be combined to increase plant growth. Highlights • Both the sewage-sludge biochar and the P-solubilizing Penicillium aculeatum enhanced root colonization by mycorrhiza (AM). • AM suppressed wheat growth, but contributed considerably to overall plant P uptake. • Penicillium aculeatum actively colonized both rhizosphere and bulk soil, both in the presence and absence of AM. • AM fungus Rhizophagus irregularis can be combined with P. aculeatum without showing antagonistic interactions. [ABSTRACT FROM AUTHOR]

Solanaceous species are among the>200 000 plant species worldwide forming a mycorrhiza, that is, a root living in symbiosis with soil-borne arbuscular-mycorrhizal (AM) fungi. An important parameter of this symbiosis, which is vital for ecosystem productivity, agriculture, and horticulture, is the transfer of phosphate (Pi) from the AM fungus to the plant, facilitated by plasma membrane-spanning Pi transporter proteins. The first mycorrhiza-specific plant Pi transporter to be identified, was StPT3 from potato [Nature414(2004) 462]. Here, we describe novel Pi transporters from the solanaceous species tomato, LePT4, and its orthologue StPT4 from potato, both being members of the Pht1 family of plant Pi transporters. Phylogenetic tree analysis demonstrates clustering of both LePT4 and StPT4 with the mycorrhiza-specific Pi transporter fromMedicago truncatula[Plant Cell,14(2002) 2413] and rice [Proc. Natl Acad. Sci. USA,99(2002) 13324], respectively, but not with StPT3, indicating that two non-orthologous mycorrhiza-responsive genes encoding Pi transporters are co-expressed in the Solanaceae. The cloned promoter regions from both genes,LePT4andStPT4, exhibit a high degree of sequence identity and were shown to direct expression exclusively in colonized cells when fused to the GUS reporter gene, in accordance with the abundance ofLePT4andStPT4transcripts in mycorrhized roots. Furthermore, extensive sequencing ofStPT4-like clones and subsequent expression analysis in potato and tomato revealed the presence of a close paralogue ofStPT4andLePT4, namedStPT5andLePT5, respectively, representing a third Pi transport system in solanaceous species which is upregulated upon AM fungal colonization of roots. Knock out ofLePT4in the tomato cv. MicroTom indicated considerable redundancy between LePT4 and other Pi transporters in tomato. [ABSTRACT FROM AUTHOR]

Investigates the formation of phosphate (P) compounds in differently P-treated hyphae of the arbuscular mycorrhizal fungus Glomus intraradices and mycorrhizal cucumber roots. Materials and methods; Plant growth and mycorrhiza formation; Phosphate pools in mycorrhizal cucumber roots.

Discusses a study which investigated the structural and functional diversity in arbuscular mycorrhizal (AM) symbioses involving three plant species and three AM fungi. Development of external hyphae; Contribution of the mycorrhizal pathway to phosphate uptake; Relationship of AM morphotype to phosphate transfer.

Compartmented monoxenic cultures of Ri T-DNA transformed carrot roots and a symbiotic arbuscular mycorrhizal fungus demonstrated for the first time that phosphate in an organic form (32P-labelled AMP) may be hydrolysed by extra-radical mycorrhizal hyphae in the absence of other organisms, and subsequently utilized as a mineral nutrient source by the host plant after fungal transport. [ABSTRACT FROM AUTHOR]

Discusses the use of phosphorus nuclear magnetic resonance spectroscopy to study phosphate metabolism in mycorrhizal and nonmycorrhizal roots of cucumber and in external mycelium of the arbuscular mycorrhizal (AM) fungus Glomus intraradices. Phosphates of nucleoside triphosphates and nucleoside diphosphates; Kinetic behavior of phosphorus uptake; Cytoplasmic volume in AM fungus.

Development of infection by vesicular-arbuscular mycorrhiza (VAM) was studied in some field-grown crops. An infection plateau was reached within the first month after seedling emergence of spring barley, oats and peas. During the rest of the growth period the proportion of root length infected by VAM remained at about 50 % in the cereals and 75 % in the peas.. In the spring, infection levels were low in winter wheat, winter rye and winter barley, and development of infection was slower in them than in the spring-sown crops. VAM infection was also studied in relation to soil depth and root density. The proportion of root length infected decreased markedly below 40 cm soil depth.. Root density varied greatly between crops, whereas the absolute length of infected roots was similar in all crops. This indicates that susceptibility to infection was independent of host species. The results are discussed in relation to final phosphorus uptake and dry-matter production, and it is proposed that a relatively low soil-phosphorus availability was counterbalanced, to some extent, by a well-developed VAM infection. [ABSTRACT FROM AUTHOR]