zygos

Domain: Eukaryota
Kingdom: Fungi
Phylum: Specific phylum as per classification
Class: Specific class within the phylum
Order: Specific order within the class
Family: Specific family within the order
Genus: Specific genus within the family
Species: Specific species within the genus
Reference: Hibbett et al., 2007, "A higher-level phylogenetic classification of the Fungi", Mycological Research, 111:509-547.

Article on fungal evolution: Biological Reviews, Volume: 94, Issue: 6, Pages: 2101-2137, First published: 29 October 2019, DOI: (10.1111/brv.12550)

Factors Influenced by Transition:
- Shift to terrestrial habitats resulted in new niches/substrates and different challenges in terms of survival and dispersal.
- Chytridiomycota considered only true fungi with motile stages.
- Aquatic higher fungi (Basidiomycetes/Ascomycetes) lack motility organs, indicating a derivation from terrestrial ancestors.

Represent about 1% of all described species of fungi.
Notable for being:
- Distinctive
- Common
- Fast-growing
Ecological Role: Primary colonizers of substrates containing accessible carbon sources (e.g., sugars, starch).
The name Zygomycota derives from their sexual reproduction method:
- Fusion (Conjugation) of morphologically similar gametangia, forming Zygosporangium (teleomorph).

Known forms include both heterothallic and homothallic species.
Zygosporangia: Typically thick-walled structures.
Mycelium: Coenocytic (aseptate).
Asexual Reproduction: Through sporangiospores; absence of flagellated cells.
Emphasis on asexual characters distinguishes Zygomycota from Ascomycetes.

Comprises at least 3 distinct evolutionary lines.
Characteristics include extensive mycelia and high levels of asexual reproductive structure differentiation.
Sexual reproduction characterized by outcrossing (heterothallism), controlled by hormonal mechanisms.
Key groups:
- Mucorales: Homothallic species with relatively undifferentiated asexual reproductive structures and limited somatic growth.
- Entomophthorales: Heterothallic species featuring elaborate asexual reproduction and parasitic habits.
- Zoopagales: Heterothallic species exhibiting significant asexual reproduction and parasitic tendencies.

Contains over 300 species including common saprobes and plant/animal pathogens.
Characteristics:
- Well-developed mycelium.
- Aseptate (coenocytic) mycelium.
- Rare anastomosis (forming interconnecting networks typical of most fungi).
- Rhizoids and stolons present.

Variation seen in zygosporangia adaptations at the species level.
Contrast with anamorphs showcasing significant and unique adaptations, reflecting different evolutionary pressures.
- Long-term survival facilitated by structures with minimal surface area and thick, protective walls.
- Dispersal functionality linked to anamorphs exhibited in diverse methods.

Subsporangial Vesicle: Contains a light-sensitive retina.
Pressure Mechanism: Osmotically active compounds lead to pressure build-up, exceeding 100 lbs/in².
Upon explosion, the vesicle hurls black sporangium up to 2 m away.
Mucilaginous contents adhere to nearby vegetation, enhancing dispersal success.

Recently described in 2001, based on ssu rDNA sequences.
Comprises about 200 species.
Unique aspect: These fungi grow predominantly within the roots of a vast majority of plants and cannot be cultivated independently.
- Growth occurs mainly between root cortical cells, forming large vesicles for food storage
- Penetrate cells to form intricately branched arbuscules.

Approximately 5-10% of plant species are classified as non-mycorrhizal.
About 70% of plants form arbuscular mycorrhizae (AM mycorrhizae).
The ubiquity of this association suggests that this symbiosis originated very early in the evolution of land plants, supported by fossil evidence.

The major functional interaction involves the exchange of Carbon (C) for Phosphorus (P); the benefits to the plant may not be as obvious as those to the fungus.
P ions are exceptionally immobile in soil, forming insoluble complexes with dominant soil cations, leading to slow diffusion rates.
As plant roots absorb P, a depletion zone is created around them.
Fungal Role: The fungus extends beyond this depletion zone, capturing essential P elements, effectively a much lower cost in hyphal construction compared to root structures (approximately 100x less).

One hypothesis suggests that the ancestral fungus might have been a pathogen.
- It would invade living plant tissues but encounter difficulties due to phosphorus deficiency.
- The fungus would import phosphorus through a hyphal network with some leaking, which was then captured by the plant.

General Characteristics:
- Only members of Kingdom Fungi possessing motile cells (zoospores and gametes) with a single, posterior whiplash flagellum.
- The thallus, hypha, or mycelium is coenocytic.
- Presence of chitinous cell walls.
- Morphological characters may vary significantly and are not reliable indicators (e.g., zoospore ultrastructure).

Habitats include aquatic and terrestrial ecosystems.
Variety of ecological roles: saprobes, parasites affecting protists, invertebrates, fungi, and plants; some are anaerobic.
Descriptions convey widespread distribution but lack comprehensive data on ecological impacts; potentially act as primary invaders and decomposers of organic materials.

May serve as vectors for damaging viruses.
Parasitic on pollen grains.
Specific species, Synchytrium endobioticum, is responsible for wart disease in potatoes, though impact is generally considered negligible.

Observation of Allomyces javanicus including life stages such as hyphae and gametangia.

Ongoing research and classification information about fungi are pivotal for understanding fungal biology and their importance to ecosystems, agriculture, and medicine.
Continuous advancements in molecular techniques (e.g., rDNA sequencing) provide deeper insights into fungal phylogenetics and diversity.