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Glomeromycota

life science Maturity 9-11 Next article →

Glomeromycota is a major division within the kingdom Fungi. This group includes approximately 230 described species. Most members of this group are famous for forming arbuscular mycorrhizas, or AMs. An arbuscular mycorrhiza is a symbiotic relationship between fungi and plants. These fungi live in the roots of vascular land plants and the thalli of bryophytes. This partnership is vital for life on Earth. It is estimated that more than 80% of all plant species form these connections. Without these fungi, many plants would struggle to grow in different environments.

The mechanism of colonization is a complex biological process. It begins with spores in the soil. These spores are the key players for establishing new hosts. Spores can be moved by air or by animals that burrow in the soil. Once a spore finds a suitable host, it begins to germinate. This process depends on specific environmental conditions. These include the right temperature and the correct amount of nutrients. Host plants even secrete chemical factors. These chemicals attract and help the growing hyphae reach the root system.

Once the fungi reach the root, a specific sequence of events occurs. The hyphae, which are fungal threads, interact with the root hairs. They may also develop structures called appressoria between the epidermal cells of the root. The hyphae then extend into the cortical cells of the root. They penetrate the cell walls but do not break the inner cellular membrane. Instead, they create an internal invagination, which is a folding inward of the membrane. Inside the cell, the hyphae branch out into a structure called an arbuscule. These highly branched arbuscules allow for a two-way movement of nutrients. The plant provides carbohydrates to the fungi. In return, the fungi help the plant manage environmental stresses.

Glomeromycota can be categorized into different groups based on their biology. Most species are terrestrial and live in soils worldwide. They are also found in wetlands, such as salt-marshes, and with epiphytic plants. While most form AMs, there are exceptions. One species, Geosiphon pyriformis, does not form arbuscular mycorrhizas. Instead, it forms an endocytobiotic association with Nostoc cyanobacteria. This means the fungus lives in a close relationship with these blue-green bacteria. Current science places the Glomeromycota within the phylum Mucoromycota. Because of this, the name Glomeromycotina is used to describe the subphylum.

The history of studying these fungi has changed significantly over time. Early scientists used morphology, or the study of physical shapes, to classify them. They looked at spore clusters, which are called sporocarps. They examined wall shapes, colors, and how the fungi reacted to stains. Initially, the genus Glomus was placed in the unrelated Endogonaceae family due to superficial similarities. As researchers cleared up confusion regarding sporocarps, the Glomeromycota were given their own order. This included families like Glomaceae and Gigasporaceae. Modern molecular techniques have since caused major revisions to these classifications.

Today, scientists use genetic tools to understand these fungi more deeply. They study the small-subunit ribosomal RNA, or SSU rRNA. This gene is highly conserved, meaning it stays very similar across different species. This makes it perfect for phylogenetic studies to see how species are related. One challenge is that Glomeromycota are biotrophic. This means they require a living host to survive. Because of this, they are very hard to grow in a laboratory. Scientists have overcome this by using root cultures. They also use a method to sequence a single nucleus from a spore.

Recent research provides even more detail about their presence in nature. A metatranscriptomic survey was conducted in the Sevilleta Arid Lands. This study looked at fungal RNA in the soil. It found that 5.4% of the fungal rRNA reads belonged to Glomeromycota. This was different from older studies that used PCR, or polymerase chain reaction. Those older studies might have underestimated how many of these fungi are actually in the soil. This shows that Glomeromycota are a consistent and important part of many ecosystems. Their ability to connect with the majority of land plants makes them essential to the global food web.

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