Application of purified strigolactone as well as a synthetic derivate Gr 24 led to hyphal branching in Gigaspora margarita , however without any effect in Glomus intraradices. Strigolactones were previously used to stimulate or break the dormancy of seeds of parasitic plants, acting in a concentration-dependent and parasite species-specific manner nefkens et al. A possible interaction between mycorrhiza and parasitic plants through host plant, resulting in reduced infection by Striga of sorghum and maize colonized by Am fungi, was postulated Lendzemo et al.
Besserer et al. This widespread strigolactone perception system suggests that already the earliest land plants used this class of molecules to communicate with their symbiotic partners Akiyama et al. The intercellular hyphae develop highly branched arbuscular structures inside root cortex which penetrate root cell wall Figure 1 and then invaginate in the host plasma membrane.
The modified plant plasma membrane forms a periarbuscular membrane PAm. The branching progression of the fungus into the host cell promotes de novo synthesis of PAm constituents which expands surrounding all the arbuscule Gianinazzi-Pearson, The nutrient exchange in the plant-fungal interfaces occurs in specific sites, where nutrients are absorbed from the soil by the fungus and transferred to the host plant, which in turn deliveries sugars to the fungal cells.
Therefore, the intense flux of ions, sugars and amino acids takes place in the arbuscules and very likely in other cell-cell interfaces where plant and fungal pumps, secondary transporters and channels are functioning Figure 2. At these sites are localized the main membrane systems responsible for the ion dynamics in association and regulating directly the host plant ionome.
However, there were some difficulties to detect the respective ATPase activation at functional level mcArthur and Knowles, ; Bago et al. Using a cell fractionation technique Tani et al. It has been proposed that the relationship between long-chain and short-chain PolyPs within the host and fungi is correlated with mycorrhizal colonization Takanishi et al.
The length of polyP in mycorrhizal roots appeared to be shorter than in extraradical hyphae or in spores, indicating that Am fungus can depolymerize polyP before transfer Pi to the host plant Ohtomo and Saito, ; Takanishi et al. The poly P content increased as colonization proceeded, and was highly correlated with the weight of the colonized roots Seufferheld and Curzi, Cruz et al. The glutamine produced is fed into the anabolic arm of the urea cycle, leading to the synthesis of arginine, which is loaded into the vacuoles.
Finally, nitrogen is al. The mechanisms by which plants perceive and respond to endogenous and exogenous stimuli may depend on receptor-like proteins. Some types of receptors have been identified in EST data sets that can have a function in the plant-endophytic bacteria interaction. Protein kinases activity is antagonized by the action of protein phosphatases. The involvement of phosphatases during plant-microbe interactions has already been demonstrated.
Genes from the model legume Lotus japonicus , encoding a protein phosphatase type 2C, had enhanced expression specifically in the nodules. However, more than a few questions remain to be answered in order to utterly understand the signal transduction pathways leading to Am formation.
Certainly we will benefit from the characterization of the myc-factors, and the identification of new mutants impaired in different stages of Am development Lima et al. DMI genes were identified as those that control calcium spiking and consequently nFs signalling pathway leading to nodulation, and it was demonstrated that they are also required for mycorrhiza formation Kistner et al.
This interesting difference found by Chaboud and colleagues indicates that the bio-active molecules released by the presymbiotic mycelium may differ from the fungal signals generated following hyphopodium differentiation on the outer root surface. Plant responses to nod-factors presence occur within minutes min , including rapid changes in ion fluxes. At the top of the signal perception transduction hierarchy are nod-factor receptors, Lysm type receptor kinases. This complex was identified in L. The finding that some legume mutants unable to form symbioses with nitrogen-fixing rhizobia nod - were also unable to develop Am myc - , suggests that both symbioses share common regulatory mechanisms Lima et al.
Previously, it was postulated by A. A major factor hampering studies of the arbuscular mycorrhizal fungi, including that on the ionome and signal transduction, is the obligatory biotrophic nature of these fungi; so far, they have not been cultured in the absence of a plant host. However, in several aspects the S. Significant achievement towards our understanding of physiological role of encoded proteins was obtained by cloning of S.
Beyond the improvement of the major nutrients n, P and K, the Am fungi can play a key function in supplying micronutrients to the host plant, like Zn and Cu marschnner and Dell, However, the systems responsible for the micronutrients transport from soil to the hyphae and from the hyphae to the root cells are yet to be fully explored in mycorrhiza, and the individual genes and gene networks that influence the acquisition and utilization of these elements remain largely unknown.
The components of a novel eukaryotic heteromeric plasma membrane complex that is essential for high affinity copper transport were identified in S. Transcript profiling and a genetic screen employed to characterize the response of fission yeast cells to zinc deficiency led to identification of Zrt1, a ZiP transporter that is a central component of zinc homeostasis Dainty et al.
Besides, Zhf transporter mediates endoplasmic reticulum storage of zinc Boch et al.
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There is a growing number of evidence that calcium homeostasis has a profound effect on proton homeostasis and other ions like copper, iron and zinc Kane, , Cheng et al. These findings is not without precedence since the S.
Thus, P5- ATPases are critical for the homeostatic control of several elements such as calcium, cobalt, copper, iron, magnesium, manganese, nickel, phosphorus, potassium, selenium, sodium, sulfur and zinc. In addition to the still-open question about the signal molecules produced by Am fungi and recognized by potential receptors, the widespread presence of bacteria inside or specifically associated with Am fungi suggests that many Am symbioses are tripartite associations. Analyzing the molecular bases of the dialogue between the three partners will be an amazing challenge. The recent elucidation of the molecular identity and function of the basic components such as strigolactones, nod factors, rOS and other molecules involved in the signal transduction and energetic of mycorrhization and bacteria symbioses will expand our knowledge on the role of the signalling pathways involved in the control and regulation of these crucial plant-microorganism symbiosis.
Further comparative analysis among the genome and transcriptome of mycorrhizal fungi, host plants and the budding and fission yeasts are needed to expand the potential of these organisms as models for elucidation of the main ion transporters, enzymes and pathways that integrates the ionome and signalling of mycorrhiza. Nature Science Aslett M, Wood V. Yeast Novel functional microRNAs from virus-free and infected Vitis vinifera plants under water stress.
Pennazio, S. An enigmatic and neglected form of plant resistance to viruses. PubMed Abstract Google Scholar. Pozo, M. Unraveling mycorrhiza-induced resistance. Localized versus systemic effect of arbuscular mycorrhizal fungi on defence responses to phytophthora infection in tomato plants. Phytohormones as integrators of environmental signals in the regulation of mycorrhizal symbioses.
Pureswaran, D. Forest insects and climate change. Rahoutei, J. Inhibition of photosynthesis by viral infection: effect on PSII structure and function. Rojas, M. Roossinck Heidelberg: Springer , 27— Elevated CO 2 spurs reciprocal positive effects between a plant virus and an arbuscular mycorrhizal fungus. Salvioli, A. Symbiosis with an endobacterium increases the fitness of a mycorrhizal fungus, raising its bioenergetic potential. Sanchez-Bel, P. The nitrogen availability interferes with mycorrhiza-induced resistance against Botrytis cinerea in Tomato.
Shaul, O. Mycorrhiza-induced changes in disease severity and PR protein expression in tobacco leaves. Sikes, B. When do arbuscular mycorrhizal fungi protect plant roots from pathogens? Plant Signal. Silvestri, A. In silico analysis of fungal small RNA accumulation reveals putative plant mRNA targets in the symbiosis between an arbuscular mycorrhizal fungus and its host plant. BMC Genomics Sipahioglu, M. Biological relationship of potato virus Y and arbuscular mycorrhizal fangus Glomus intraradices in potato.
Pest Technol. Song, Y. Enhanced tomato disease resistance primed by arbuscular mycorrhizal fungus. Priming of anti-herbivore defense in tomato by arbuscular mycorrhizal fungus and involvement of the jasmonate pathway.
Spanu, P. Chitinase in roots of mycorrhizal Allium porrum: regulation and localization. Planta , — Spatafora, J. A phylum-level phylogenetic classification of zygomycete fungi based on genomescale data.
Mycologia , — Stolyarchuk, I. Virus infection course in different plant species under influenceof arbuscular mycorrhiza. Thiem, D. Interactive physiological response of potato Solanum tuberosum L.
An outlook on ion signaling and ionome of mycorrhizal symbiosis
Acta Mycol. Turina, M. The virome of the arbuscular mycorrhizal fungus Gigaspora margarita reveals the first report of DNA fragments corresponding to replicating non-retroviral RNA viruses in fungi. Turrini, A. Functional complementarity of arbuscular mycorrhizal fungi and associated microbiota: the challenge of translational research.
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