Development of Mycorrhiza and their Influence on Nutrient Status, Plant Growth and Innate Immunity (original) (raw)
Related papers
Frontiers in Microbiology, 2018
Plants do not exist as single entities but should rather be considered to form a complex community with microbes and other organisms where plant tissues form diverse niches for microbes. One major relationship concerns plant-fungal interactions that range from pathogenicity to mutually beneficial symbioses. A balanced state (homeostasis) of these interactions is essential for maintaining the plant as well as an overall healthy state of the environment. Mycorrhizal associations are well-studied examples of root-fungal mutually beneficial symbiosis (Ferlian et al., 2018; Gehring and Johnson, 2018). The reasons for establishing a mutual symbiosis are only just beginning to be understood at the molecular level (Mello and Balestrini). Communication between endo-and ecto-mycorrhiza and their respective host plants (Raudaskoski and Kothe, 2015; Luginbuehl and Oldroyd, 2017; Garcia et al., 2018, and citations therein) and the effects on phytohormone levels and localized delivery (see Boivin et al., 2016; MacLean et al., 2017) have been the focus of several recent reports. But even so, a full understanding of these relationships will only be gained by investigating the effects of different strains of the same fungal species (Sharma et al.). For roots, as well as above-ground plant tissues, endophytic fungi can be considered as examples of specific co-evolution, provided the term "endophytic" is used in its sensu strictu (for a detailed comment, see Kothe and Dudeja, 2011). To prove endophytic behavior, Koch's postulates need to be observed, and tissue specificity for re-infection may be used as a method to discriminate real endophytes from mere co-occurrence (Wȩżowicz et al., 2017; Domka et al., 2018; Ważny et al., 2018). The traits of endophytes that do not lead to symptoms in a healthy plant clearly delineate them from phytopathogenic fungi, however, caution is necessary because their effect on the symbiosis can vary with the species/variety of the partner and environmental conditions. For endophytic fungi, knowledge is much more limited as compared to mycorrhiza, although a role for strigolactone signaling is presented by Rozpądek et al. Temporal shifts in plant-associated fungal populations are known to occur. An example from mycorrhizal symbiosis is for young trees with endomycorrhizal symbionts that are later replaced by specific ectomycorrhizal associations (Knoblochová et al., 2017; Bachelot et al., 2018). Within 4 weeks, vesicles and hyphae are visible in the roots of Picea abies and Pinus sylvestis leading to increased main-root development and up to a 300% increase in secondary roots.
Arbuscular mycorrhizae in plant survival strategies
Mycorrhizae have been associated with vascular plants since the Palaeozoic times. The colonization of terrestrial ecosystems by the ancestors of modern vascular plants was facilitated by symbiotic fungi similar to modern endomycorrhizae. Arbuscular Mycorrhizae (AM) comprise of over 150 species that are not host specific and form symbiotic associations with a wide range of host species. AM bestow a selective advantage on their host over competing non-host species by making available nutrients, providing defence against several pathogenic organisms and by influencing the composition of the microflora of the rhizosphere. However, the benefits that AM provides to its host come with a price tag. The plant has to forego up to 10-20% of its photosynthetic produce to maintain the fungus. This review discusses the conditions under which forming an AM association would be a competitively advantageous strategy for the host plant.
The arbuscular mycorrhizal (AM) symbiosis is the association between fungi of the order Glomales (Zygomycetes) and the roots of terrestrial plants (Harley and Smith, 1983). Conservative estimates suggest that this ancient symbiosis, dating back to the early Devonian age (398 million years ago), affects approximately 90% of the Earth's land plant species . This symbiosis is increasingly being recognized as an important and integral part of natural ecosystems throughout the world. The AM fungus-plant association is a mutually beneficial event: The plant supplies the fungus with carbon (from its fixed photosynthates) while the fungus assists the plant in its uptake of phosphate and other mineral nutrients from the soil (Smith and . This bidirectional exchange of nutrients takes place through extensively branched haustoria, termed arbuscules. In addition to increased nutrition, mycorrhizal plants also show increased resistance to root pathogens and tolerance to drought stress, and their hormonal balance is altered (Smith and Hwang et al., 1992).
Regulation of Root and Fungal Morphogenesis in Mycorrhizal Symbioses
Plant Physiology, 1998
The root-fungus symbioses called mycorrhizas have been known and studied since the last century. Currently, four main types of mycorrhiza are recognized, based pri- marily on the fungal partner in the association and the types of mycorrhizal structures that develop. In all mutu- alistic types, the mycorrhizal association contributes signif- icantly to the mineral nutrition of the plant host, in
2021
This review analyzes the physiological, biochemical and molecular implications related to the interaction between arbuscular mycorrhizal fungi (AMF) and plants in the pre-symbiotic and symbiotic stages. Factors involving spore germination, germ tube growth, signaling and recognition of mycorrhizal fungi are discussed from a macro context, in which the plant interacts with the environment, to a most intrinsic context, in which genes are involved in this interaction. The colonization stages, from the formation of hyphopodium to the differentiation of arbuscules, are described according to cellular changes and molecular mechanisms. The dynamics of nutrient exchanges are discussed bidirectionally, from the fungus to the plant and from the plant to the fungus. The regulation processes of absorption and transport of water, phosphorus, nitrogen and calcium, and carbohydrates via the periarbuscular membrane are described in cellular, functional and molecular terms. The most common changes in the secondary metabolism of plants associated to AMF are also presented, based on biochemical processes. The conjuncture analysis showed that in the last decade, studies made efforts to identify the mechanisms of communication and symbiosis functioning, differently from studies carried in the past decades, which extensively investigated the aspects related to the growth responses of symbionts, especially in plants.