Dolipore septum of Basidiomycetes

Dolipore septa are particular cell partitioning dividers. These are present in almost every form of fungus. This dolipore septum structure is often capped on either side by the brackets, which are specific layers of cells. Royall Moore and James McAlear, two scientists, were the first to depict this structure. The dolipore septum is a distinctive structural structure present in the hyphal cells of Basidiomycetes, a fungal group that includes mushrooms, toadstools, and a variety of other well-known fungi. Therefore, septum is essential for the growth and development of these fungi.

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Dolipore septum:

The septa of Dolipore change dramatically between monokaryotic and dikaryotic hyphae. They originate at distinct stages of the basidiomycete life cycle. The parenthesomes are continuous with the endoplasmic reticulum in monokaryotic hyphae but not in dikaryotic hyphae. Further, the septal walls are made of a different substance than the cell walls. All dolipore septa enable cytoplasm and occasionally mitochondria to pass through their pores; those in monokaryotic hyphae feature perforated parenthesomes that allow cell nuclei to pass through as well.

Structural Features:

• They contain a central pore which permits cytoplasmic continuity between the adjacent segments. The septal pore is generally surrounded by barrel-shaped thickened wall material.
• The centripetal ingrowth of a membrane which has glucan and chitin wall material deposited on both faces, initiates septal development.
• Septa develop synchronously in the main hypha and clamp and are finished in a matter of minutes. They are formed by the plasma membrane furrowing and concomitant wall deposition. Fine filaments form a ring around the deposited septum.
• The pore opening has shrunk to around 140 nm and there is still no parenthesome covering it, indicating that this is a late stage in septal pore formation. At maturity, the pore is bordered on each side by a dome-shaped, perforate parenthesome.
• Filaments emanate from this substance and make touch with the parenthesome. The entire structure is understood as a coordinated whole, with the radiating filaments anchoring and supporting the parenthesome to preserve its form, location, and orientation in reference to the pore opening.
• The thickening around the pore results from rapid deposition of wall material. However, very thick pore rims may can be a reason associated with the fixation of chemicals.

Dolipore septum in Basidiomycetes:

• Basidiomycetes are one of two main divisions that make up the subkingdom Dikarya within the kingdom Fungi, along with Ascomycetes.
• Instead of being enclosed within cells, spores of basidiomycetes form on projections that shoot out from microscopic cells called basidia. The basidia are often elongated and club-like.
• Doliopore septum is a Basidiomycete feature, i.e. Dolipore septa are specialised dividing walls between cells (septa) present in practically all species of fungus in the phylum Basidiomycota.
• They feature a barrel-shaped swelling around their central pore, which is around 0.1-0.2 m broad, unlike other fungal septa. As a result, this septum is unique to Basidiomycetes.

Image source: Bloemendal, S., & Kück, U. (2013). Cell-to-cell communication in plants, animals, and fungi: a comparative review. Naturwissenschaften, 100, 3-19.

Characteristics and Functions

Filamentous fungi have septa with a central pore that compartmentalises their hyphae. The fungal septa and septum-associated structures help to maintain cellular and intrahyphal equilibrium. Dolipore septa in the upper Basidiomycota (Agaricomycotina) are connected with septal pore caps. Despite substantial research into the ultrastructure of septal pore caps, little is known about their biological content or function. The structure of the Dolipore septa changes significantly in both monokaryotic and dikaryotic hyphae, with different foci throughout basidiomycete life cycles. In monokaryotic hyphae, parentheses remain with the endoplasmic reticulum, and septal dividers are formed from unexpected materials compared to the cell walls.

Significance of Dolipore septum in Basidiomycetes:

The dolipore septum is a significant component in the development of basidiospores, controlling the movement of nutrients, cytoplasm, and nuclei within the basidium. It plays a vital role in maintaining the dikaryotic stage and is essential for understanding fungal ecology and nutrition. Its anatomy and function are crucial for mycological studies and biotechnological applications.

Dolipore septa in basidiomycete hyphae differ markedly between monokaryotic and dikaryotic forms. Monokaryotic hyphae feature parentheses that connect to the endoplasmic reticulum, as well as distinct septal walls. All dolipore septa enable cytoplasm and mitochondria to pass through their pores, whereas monokaryotic hyphae contain perforated parenthesomes. Therefore, it is a distinguishing and important property of Basidiomycete fungus biology and classification.

REFERENCES:

1. Orlovich, D.A., Ashford, A.E. Structure and development of the dolipore septum inPisolithus tinctorius . Protoplasma 178, 66–80 (1994). https://doi.org/10.1007/BF01404122

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