Mycorrhiza
[9] The 400 million year old Rhynie chert contains an assemblage of fossil plants preserved in sufficient detail that arbuscular mycorrhizae have been observed in the stems of Aglaophyton major, giving a lower bound for how late mycorrhizal symbiosis may have developed.
[27] The ectomycorrhizal fungus Laccaria bicolor has been found to lure and kill springtails to obtain nitrogen, some of which may then be transferred to the mycorrhizal host plant.
In a study by Klironomos and Hart, Eastern White Pine inoculated with L. bicolor was able to derive up to 25% of its nitrogen from springtails.
[28][29] When compared with non-mycorrhizal fine roots, ectomycorrhizae may contain very high concentrations of trace elements, including toxic metals (cadmium, silver) or chlorine.
[31] An expansion of several multigene families occurred in this fungus, suggesting that adaptation to symbiosis proceeded by gene duplication.
Within lineage-specific genes those coding for symbiosis-regulated secreted proteins showed an up-regulated expression in ectomycorrhizal root tips suggesting a role in the partner communication.
By contrast, L. bicolor possesses expanded multigene families associated with hydrolysis of bacterial and microfauna polysaccharides and proteins.
This genome analysis revealed the dual saprotrophic and biotrophic lifestyle of the mycorrhizal fungus that enables it to grow within both soil and living plant roots.
Since then, the genomes of many other ectomycorrhizal fungal species have been sequenced further expanding the study of gene families and evolution in these organisms.
The structure of the arbuscules greatly increases the contact surface area between the hypha and the host cell cytoplasm to facilitate the transfer of nutrients between them.
Fossil evidence[6] and DNA sequence analysis[37] suggest that this mutualism appeared 400-460 million years ago, when the first plants were colonizing land.
[19] The hyphae of arbuscular mycorrhizal fungi produce the glycoprotein glomalin, which may be one of the major stores of carbon in the soil.
[38] Arbuscular mycorrhizal fungi have (possibly) been asexual for many millions of years and, unusually, individuals can contain many genetically different nuclei (a phenomenon called heterokaryosis).
This group of mycorrhizal fungi is little understood, but appears to prefer wet, acidic soils and forms symbiotic relationships with liverworts, hornworts, lycophytes, and angiosperms.
Plants that form ericoid mycorrhizae are mostly woody understory shrubs; hosts include blueberries, bilberries, cranberries, mountain laurels, rhododendrons, heather, neinei, and giant grass tree.
Orchid seeds are so small that they contain no nutrition to sustain the germinating seedling, and instead must gain the energy to grow from their fungal symbiont.
[17] The OM relationship is asymmetric; the plant seems to benefit more than the fungus, and some orchids are entirely mycoheterotrophic, lacking chlorophyll for photosynthesis.
In the OM symbiosis, hyphae penetrate into the root cells and form pelotons (coils) for nutrient exchange.
[45] It has also been suggested that evolutionary and phylogenetic relationships can explain much more variation in the strength of mycorrhizal mutualisms than ecological factors.
While the signals emitted by the fungi are less understood, it has been shown that chitinaceous molecules known as Myc factors are essential for the formation of arbuscular mycorrhizae.
AMF genomes also code for potentially hundreds of effector proteins, of which only a few have a proven effect on mycorrhizal symbiosis, but many others likely have a function in communication with plant hosts as well.
[55] The mycorrhizal mutualistic association provides the fungus with relatively constant and direct access to carbohydrates, such as glucose and sucrose.
[57] Unaided plant roots may be unable to take up nutrients that are chemically or physically immobilised; examples include phosphate ions and micronutrients such as iron.
[62] Suillus tomentosus, a basidiomycete fungus, produces specialized structures known as tuberculate ectomycorrhizae with its plant host lodgepole pine (Pinus contorta var.
[64] More recent studies have shown that mycorrhizal associations result in a priming effect of plants that essentially acts as a primary immune response.
[66] Furthermore, mycorrhizal fungi was significantly correlated with soil physical variable, but only with water level and not with aggregate stability[67][68] and can lead also to more resistant to the effects of drought.
[69][70][71] Moreover, the significance of mycorrhizal fungi also includes alleviation of salt stress and its beneficial effects on plant growth and productivity.
Another study discovered that zinc-tolerant strains of Suillus bovinus conferred resistance to plants of Pinus sylvestris.
"[85] A company in Israel, Groundwork BioAg, has discovered a method of using mycorrhizal fungi to increase agricultural crops while sequestering greenhouse gases and eliminating CO2 from the atmosphere.
SPUN is a science-based initiative to map and protect the mycorrhizal networks regulating Earth’s climate and ecosystems.
