Mycorrhizal symbiosis pdf


PDF | On Jan 1, , Omid Alizadeh and others published Mycorrhizal symbiosis. PDF | Reproduction is an essential function of all organisms and, for many crop Still, relatively little is known about the effects of the mycorrhizal symbiosis on. Rrhiza meaning root and its' meaning in reality means symbiosis between a fungus overview on the mycorrhizal symbiosis and Classification of mycorrhiza.

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Mycorrhizal Symbiosis Pdf

The mycorrhizal symbiosis is arguably the most important symbiosis on earth. mycorrhizal fungus provides the host plant with nutrients, such as phosphate. Recent years have seen extensive research in the molecular underpinnings of symbiotic plant-fungal interactions. Molecular Mycorrhizal. Arbuscular mycorrhizal symbiosis and ecosystem processes: Prospects for future research in tropical.

Nearly all phytohormones are employed by plants to regulate the symbiosis with AM fungi, but the regulatory role of cytokinin CK is not well understood. Here, we used transgenic tobacco Nicotiana tabacum with a root-specific or constitutive expression of CK-degrading CKX genes and the corresponding wild-type to investigate whether a lowered content of CK in roots or in both roots and shoots influences the interaction with the AM fungus Rhizophagus irregularis. Our data indicates that shoot CK has a positive impact on AM fungal development in roots and on the root transcript level of an AM-responsive phosphate transporter gene NtPT4. A reduced CK content in roots caused shoot and root growth depression following AM colonization, while neither the uptake of phosphorus or nitrogen nor the root transcript levels of NtPT4 were significantly affected. This suggests that root CK may restrict the C availability from the roots to the fungus thus averting parasitism by AM fungi. Taken together, our study indicates that shoot- and root-borne CK have distinct roles in AM symbiosis. We propose a model illustrating how plants may employ CK to regulate nutrient exchange with the ubiquitous AM fungi. Electronic supplementary material The online version of this article doi Keywords: Nicotiana tabacum, Rhizophagus irregularis, Symbiosis, Cytokinin, Carbon, Phosphate transporter genes Introduction The arbuscular mycorrhizal AM symbiosis, a widespread association between terrestrial plants and fungi of the phylum Glomeromycota, is regulated from the plant side by nearly all known phytohormones Bucher et al. Yet, the function of CK in AM symbioses is poorly understood. The AM fungi are obligate biotrophs that obtain photosynthetically fixed carbon C in colonized roots via transport of sugars from root cortex cells to the intracellular arbuscules in the apoplast of the root cortex cells and to the intercellular hyphae Helber et al. In exchange, the AM mycelium spreading into the soil takes up mineral nutrients particularly phosphorus P , along with nitrogen N and other minerals, transports them through their hyphae towards the root, and delivers them via the arbuscules into the surrounding plant cells Marschner ; Nouri et al. The mycorrhizal delivery of P is regulated by the root through particular phosphate Pi transporter PT genes Maeda et al. The direct pathway for Pi uptake via root hairs and epidermis may be, in some cases, suppressed by AM colonization Chen et al. Despite the reciprocal nutritional benefit, the plant growth response to AM colonization can range from positive to negative according to a mutualism-parasitism continuum Johnson

Moreover, mycorrhiza-formation genes from Mucoromycotina-associated liverworts recover the Glomeromycotina-associated phenotype in a transformed mutant of the angiosperm Medicago truncatula, which reveals that the genes required for symbiosis have been conserved among liverworts that associate exclusively with Mucoromycotina as well as higher plants that associate exclusively with Glomeromycotina 13 , Given that Ascomycota, Basidiomycota, Glomeromycotina, and Mucoromycotina likely diverged prior to the divergence of land plants 22 , 23 , it is possible to treat different combinations of symbiotic association with these phyla as categorical character states on the plant phylogeny and analyse transition dynamics between the states in a Bayesian phylogenetic comparative context.

Considering the uncertainty of the evolutionary relationships of early Embryophytes 24 , 25 , we assessed the probability of all possible combinations of mycorrhizal associations for the most recent common ancestor of land plants. Results We obtained a dataset of species of land plants for which the mycorrhizal fungi have been identified with molecular methods. We used the plant chloroplast DNA markers psbA, rbcL and rps4 to infer phylogenetic relationships between these species.

Our estimates of phylogeny correspond well with the prevailing understanding of the systematics of the land plants at least so far as the monophyly of major groups and the relative branching order of these groups under the different rooting scenarios are concerned 26 , Optimising the observed repertoires of mycorrhizal association as transitioning categorical states on our phylogenetic estimates resulted in a general pattern of phylogenetic conservatism: major plant groups associate quite uniformly with major fungal groups Fig.

Our ancestral state reconstructions recover strong support for the presence of mycorrhiza-like association for the most recent common ancestor of the land plants. Figure 1 Evolution of mycorrhiza-like associations in land plants.

Branches are coloured according to the most probable state of their ancestral nodes.

Main plant lineages are marked with black labels. Branch lengths represent time in million years. Bar is 50 million years.

Full size image The pattern of transitions among different repertoires of symbiotic association suggests two main paths along which individual associations within a larger repertoire are gained and lost relatively promiscuously Fig. The first of these paths involves Mucoromycotina and Glomeromycotina: the association with Glomeromycotina is added to, and subtracted from, the association with Mucoromycotina at relatively high instantaneous transition rates.

The association with Mucoromycotina within a repertoire that spans both is also lost at relatively high rates, but gained at much lower rates, suggesting that the association with Glomeromycotina is relatively more facultative within this repertoire.

The second path includes gains and losses of Ascomycota, and losses of Glomeromycotina but gains less so , at high rates within repertoires in which the association with Basiodiomycota appears more obligate.

Figure 2 Transitions of mycorrhiza-like associations in land plant evolution. Frequency of transitions between different repertoires of mycorrhiza-like association as optimised on our phylogeny Fig. The band size for each state labelled next to the bands represents the number of transitions from that state proportional to the total number of reconstructed transitions; and the width of the ribbons is proportional to the numbers of transitions starting from that state.

Placing the evolution of mycorrhizal associations on a temporal axis in a sliding window analysis Fig. Figure 3 Evolution of mycorrhiza-like associations through time. The proportion of each mycorrhizal state relative to the total number of branches at that particular point in time, sampled at 50 million year intervals on our phylogeny with ancestral state reconstructions Fig.

Full size image Discussion For each evaluated scenario of land plant evolution, our results support the hypothesis that the most recent common ancestor of land plants was involved in symbiotic interactions with fungi.

Shoot- and root-borne cytokinin influences arbuscular mycorrhizal symbiosis

This result is in accordance with evidence from the fossil record 11 and genomics 12 , 13 , For the small, rootless, leafless plants with rhizoid-based absorbing systems that started colonizing the land, the alliance with fungi is hypothesized to have been essential in overcoming major issues of nutrient and water limitation in the absence of existing soils 29 , Our analyses suggest that the fungal associates of these earliest land plants most likely included Mucoromycotina, and not exclusively Glomeromycotina, as commonly assumed 1 , 31 , An exclusive association with Mucoromycotina for the root of the land plants received the highest support of all possible mycorrhizal repertoires, for all hypotheses of the relationships between the main land plant lineages.

Furthermore, our hypothesis tests supported Mucoromycotina over Glomeromycotina as the initial gain for the most recent common ancestor of the land plants. However, our reconstructions also suggest that a repertoire comprising both Mucoromycotina and Glomeromycotina cannot be ruled out, and we find high rates for transitions in which Glomeromycotina are gained and lost in combination with Mucoromycotina Fig.

Mucoromycotina have been recorded in the rhizoids and roots of extant liverworts 16 , hornworts 18 , lycophytes 21 , ferns 21 , gymnosperms 33 , 34 , and angiosperms 35 , but within early diverging land plant lineages except for the liverwort lineage Haplomitriopsida 16 they were mostly found simultaneously with Glomeromycotina 16 , 18 , The association with both fungal lineages was likely also present in the Devonian fossil plant Horneophyton ligneri 11 , and Field et al.

However, this plasticity appears to not be maintained: once association with Mucoromycotina is lost, reversals occur at a low rate Fig.

The scenario presented here is contingent on our current understanding of the early diversification of fungi and plants. Both Mucoromycotina and Glomeromycotina are part of the monophyletic phylum Mucoromycota 10 , and their divergence has been estimated to predate the colonization of land by plants However, extant symbiotic species of Mucoromycotina are part of the order Endogonales 10 , 16 , 36 and the phylogenetic position of this group — and thus the timing of its origin relative to the emergence of land plants — remains to be investigated.

Under this alternative scenario, symbioses formed by Mucoromycotina and Glomeromycotina result from a single evolutionary event within fungi, and, consequently, this would imply that other nutritional strategies within Mucoromycota mostly plant pathogens and decomposers 10 represent derived states within this group.

Water relations, drought and vesicular-arbuscular mycorrhizal symbiosis | SpringerLink

Under our current understanding of the evolution and nutritional modes of early diverging fungi, this scenario is unlikely From the prevalent association with strictly Glomeromycotina, there have been multiple independent evolutionary shifts towards Ascomycota and Basidiomycota, leading to increasingly prevalent reconstruction of these interactions over the course of plant diversification Fig.

Our results suggest that these transitions started with a gain of Basidiomycota, rather than Ascomycota Fig.

Subsequent gains of Ascomycota and losses of Glomeromycotina occur at high rates, leading to various association repertoires that include either or both Ascomycota and Basidiomycota. These repertoires are present in several extant land plant lineages and represent the ectomycorrhizal, orchid mycorrhiza, and ericoid mycorrhizal types 9 , The ability to recruit saprotrophic lineages of wood and litter decaying fungi from among Ascomycota and Basidiomycota into novel symbioses was likely instrumental for plant adaptation to various ecological challenges 5.

For example, for Orchidaceae, the most species-rich lineage of non-arbuscular mycorrhizal plants, the transition from associations with Glomeromycotina to Ascomycota and Basidiomycota is linked to niche expansions and radiations, which in synchrony with the development of specialized pollination syndromes has promoted speciation in the largest family of plants on earth 38 , Similarly, the independent evolution of ericoid mycorrhiza in Diapensiaceae and Ericaceae, estimated to date back to the Cretaceous 40 , 41 , is a potential adaptation to nutrient poor, acidic soils Also, transitions to ectomycorrhiza independently evolved in various gymnosperm e.

Pinaceae, Gnetum, Taxus and angiosperm lineages e. Parallel to the latter, a shift towards fungi involved in the ectomycorrhizal and ericoid symbiosis has also occurred in liverworts Fig. Although relatively few plant species — mostly trees and shrubs — are ectomycorrhizal, the worldwide importance of the ectomycorrhizal association is considerable, due to its dominance in temperate and boreal forests, and in tropical rainforests in Southeast Asia Ectomycorrhizal symbioses likely emerged in semi-arid forests dominated by conifers under tropical to subtropical climates and diversified in angiosperms and conifer forests driven by a change to cooler climate during the Cenozoic 42 , Loss of mycorrhizal symbiosis has occurred from all single association states, mostly at relatively low transition rates Fig.

These transitions are explained by plant adaptations to either nutrient-rich or extremely nutrient-poor soils, for which the benefits of the symbiosis do not outweigh its costs However, transition rates towards the non-mycorrhizal state may have been underestimated here, since several non-mycorrhizal angiosperm lineages all with a recent evolutionary origin 45 have not been included.

A notable increase in the proportion of non-mycorrhzial lineages around mya is caused by the origin of mosses and the diversification of non-mycorrhizal liverworts. Similar to Maherali et al. Because it is not known whether the mycorrhizal symbiosis can be recovered after loss, it is possible that this pathway may not occur in nature.

In most plant lineages, Glomeromycotina, the dominant mycorrhizal symbionts of extant land plants, subsequently replaced Mucoromycotina. Later on, several transitions from Glomeromycotina to various Ascomycota and Basidiomycota lineages have occurred, establishing novel mycorrhizal syndromes, such as orchid, ericoid, and ectomycorrhizas.

Our findings demonstrate the importance of Mucoromycotina fungi for our understanding of the early evolution of the mycorrhizal symbiosis. We still know very little about the biology of symbiotic Mucoromycotina 36 , but experimental evidence suggests they form mycorrhizas that are physiologically and functionally different from symbioses with Glomeromycota In this study, maize plants were grown in pots with sterile river sand containing FePO4 and were inoculated with the mycorrhizal fungus Rhizophagus irregularis.

The plants were grown under S deficient conditions until day 60 from sowing and on that day sulfate was provided to the plants. In addition, total shoot Fe concentration was determined before and after S supply.

AM symbiosis prevented Fe deprivation responses in the S deprived maize plants and iron was possibly provided directly to the mycorrhizal plants through the fungal network. Furthermore, sulfate possibly regulated the expression of all three genes revealing its potential role as signal molecule for Fe homeostasis. Keywords: maize, arbuscular mycorrhizal symbiosis, sulfur, iron homeostasis, nicotianamine synthase, yellow stripe Introduction Iron is an essential micronutrient for plants.

Graminaceous plants follow the Strategy II for iron acquisition from the rhizosphere.

Iron homeostasis in maize involves a series of processes, including the biosynthesis of deoxymugineic acid DMA for iron uptake from the rhizosphere and the translocation of iron throughout the plant body toward the sink organs Kobayashi et al. In this iron uptake pathway, three molecules of S-adenosyl-methionine are combined to form nicotianamine NA which is then used as the precursor for DMA biosynthesis.

Evolutionary dynamics of mycorrhizal symbiosis in land plant diversification

In addition to its role in iron uptake, NA plays also a dominant role in iron transfer, being used for the intercellular and intracellular Fe transport in all plants' organs, as well as long distance transport through the phloem Kobayashi et al. The primary precursor of NA is methionine, a sulfur-containing amino acid, so sulfur deprivation has a strong effect on iron homeostasis; as a result, S deficiency causes Fe deprivation responses to the graminaceous plants, which can be inverted when S is provided Astolfi et al.

The strong connection between sulfur and iron is typified by the Fe-S clusters, where most of the metabolically active Fe is bound to S. In chloroplasts, the most abundant Fe-S proteins are ferredoxin, photosystem I and cytochrome b6f complex. This connection between the two nutrients suggests coordination between the metabolisms of S and Fe Forieri et al. Recent studies revealed the evolutionary relationship and tissue specific expression profiles of ZmNAS genes in maize leading to their grouping into two classes.

These NAS genes are important for local iron distribution in leaves and sheaths and play a key role in iron homeostasis and detoxification Mizuno et al. ZmYS1 is a membrane protein and functions as a proton-coupled symporter that mediates iron uptake in maize.

ZmYS1 expression at both the mRNA and protein levels responds rapidly to changes in iron availability, whilst it is not regulated by zinc or copper deficiency Curie et al. Arbuscular mycorrhizal AM symbiosis improves plant nutrient uptake under low nutrient availability Bonfante and Genre, The role of AM symbiosis on phosphate has been extensively studied Smith et al.

Moreover, other nutrients such as nitrogen and sulfur are shown to be translocated from the fungal to the plant partner Ames et al.