Reproduction of sexual, asexual and parasexual fungi

4151
David Holt
Reproduction of sexual, asexual and parasexual fungi

The reproduction of the funguss it is the biological event by which all fungi multiply. The different species of fungi can reproduce through sexual or asexual reproduction or through both types of reproduction at the same time..

Some fungi reproduce exclusively asexually. However, there are some, such as yeasts, for example, that can go long periods of time without reproducing sexually and can give the impression that they reproduce exclusively asexually..

Mushroom life cycle

In general, fungi have a rapid reproduction that allows them to adapt, colonize and spread in a short time in practically any environment that has moderately ideal conditions for their development..

All fungi are taxonomically classified within the Fungi Kingdom. Many of them are free-living, others are plant and / or animal pathogens, and others live in association with other living beings (such as symbionts, for example).

Most of the sanitary measures in the food industry, especially those related to the production and packaging of bread, dairy products, fruits and vegetables, focus on avoiding the colonization, growth and, above all, the reproduction of fungi. and potentially pathogenic bacteria in these foods.

Article index

  • 1 Sexual reproduction of fungi
    • 1.1 Species of dioecious fungi
    • 1.2 Fusion of two nuclei
    • 1.3 How is the process?
  • 2 Asexual reproduction of fungi
    • 2.1 Conidium
    • 2.2 Conidiogenesis
  • 3 Parasexual reproduction of fungi
  • 4 Other forms of asexual reproduction in fungi
  • 5 References

Sexual reproduction of fungi

Sexual reproduction in a basidiomycete (Source: LaNitaRi, via Wikimedia Commons)

Sexual reproduction in fungi is described in some texts as "perfect reproduction." This is produced by two differentiated cells called gametes or gametes that, in turn, are produced by cells called gametangia.

Gametangia can be isogamous and produce isogametes, that is, they are structures that produce gametes morphologically indistinguishable between both sexes. Otherwise they can be heterogametic and produce heterogametes (different gametes).

Heterogametic gametangia produce male and female gametes, and both cells are morphologically different. In this case, the male gametes are known as antheridia and the female ones as oospores..

Dioecious fungal species

Mushrooms in forest

Generally, the heterogametic fungal species that produce gross male and female sexual structures are known as dioecious fungal species. In these cases the fungi only produce the sexual organs in the presence of an individual of the opposite sex..

Despite the above, it is common for the same individual to carry the male and female sexual organs, and that is why some fungi are considered hermaphroditic organisms..

Fusion of two nuclei

As in all eukaryotic organisms, sexual reproduction in fungi involves the fusion of two cell nuclei with half the chromosomal load of the individual (s) that produce them, which necessarily implies a prior meiosis process to reduce said genetic load..

How is the proccess?

Sexual reproduction is a process that ensures the production of new genetic combinations within fungal populations.

Usually these novel combinations allow them to acquire the necessary changes in genetic information to adapt to new environments that have challenging conditions for their survival..

Sexual reproduction in fungi consists of three processes: plasmogamy, karyogamy and meiosis, namely:

- Plasmogamy

It is the fusion between the cell membranes of the two gametic cells with a haploid nuclear charge (n). This fusion of the membranes allows the two nuclei of the gametic cells to approach and later fuse.

- Karyogamy

In karyogamy, the fusion of the two gametic nuclei (n) originates a diploid nucleus (2n) called a zygote. The zygote is a well-defined uniform mass of genetic material that can be easily seen with a light microscope..

- Meiosis

Meiosis occurs to restore the haploid condition of the gametic nuclei. The fusion of the two haploid nuclei gives rise to 4 new recombinant haploid nuclei (n).

If unfavorable conditions occur during sexual reproduction, some species of fungi can delay or slow down the meiosis process and remain for long periods of time in a diploid phase (2n) or dikaryotic (n + n) that is, with two haploid nuclei.

Sexual reproduction culminates in the production of spores that tend to group together in structures known as sporangia..

Microscopic view of the sporangium of a fungus. Source: Juan Carlos Fonseca Mata / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

Asexual reproduction of fungi

Asexual reproduction of fungi occurs much more frequently than sexual reproduction. These organisms, under normal conditions, reproduce constantly through spores produced by asexual reproduction..

Through asexual multiplication, fungal species can spread rapidly, since they produce many spores at the same time in each reproduction cycle. In addition, they can perform several cycles of reproduction in short periods of time..

Conidium

Conidia at the end of a conidiophore. Source: Emmanuel Boutet / CC BY-SA (https://creativecommons.org/licenses/by-sa/2.5)

In some texts asexual reproduction is described as "anamorphic reproduction". This type of reproduction produces a large number of spores that generally group together forming a structure called conidia..

Each conidia spore is different depending on the species of fungus, but all the conidia are full of spores that will form new fungi, which will be clones of the fungus that synthesized the spores, that is: genetically identical to the "parent" fungus.

Spores are produced through mitosis events and fungi that only reproduce by this process are known as mitosporic. However, many species of fungi are mythosporic for long periods of time and then reproduce sexually (we could say that meiosporic).

Conidiogenesis

Generally, asexual reproduction occurs in specialized cells of fungi called conidiogenic cells, which are formed through a process called conidiogenesis..

Conidiogenesis can occur in two different ways: thalic conidiogenesis and blast conidiogenesis..

- Thalic conidiogenesis: many cells of the fungus differentiate into conidiogenic cells and then develop into different conidia.

- Blast conidiogenesis: a bump or gem that arises in the conidiogenous cell differentiates into a conidia.

Parasexual reproduction of fungi

In some species of fungi it has been observed that recombination (mixing of the genetic material between chromosomes) typical of sexual reproduction (meiosis) can occur but during mitotic reproduction.

This type of reproduction is called parasexual reproduction and is frequent in many species of fungi and some of bacteria..

Parasexual reproduction involves the fusion of two genetically different haploid nuclei (n) to form a diploid nucleus (2n) that then undergoes a loss of genetic load until it becomes haploid (n) again, but with different genetic information to any of the parental nuclei.

Parasexual reproduction is very particular in nature and it is not yet understood why it occurs, or many of its mechanisms.

However, this type of reproduction helps many species of fungi that only reproduce clonally (asexually) to increase their rate of genetic variability in the absence of the meiosis characteristic of sexual reproduction..

Other forms of asexual reproduction in fungi

Budding of a yeast (Source: Pngbot, via Wikimedia Commons)

Some fungi such as yeast reproduce simply by budding, binary fission, or fragmentation. All these processes occur by the simple division of a cell to give independence to the newly originated cell. It is characteristic of unicellular fungus.

References

  1. Heitman, J., Sun, S., & James, T. Y. (2013). Evolution of fungal sexual reproduction. Mycology, 105(1), 1-27.
  2. Kuhar, J. F., Castiglia, V. C., & Papinutti, V. L. (2013). Kingdom Fungi: morphologies and structures of fungi.
  3. Petersen, J. H. (2013). The kingdom of fungi. Princeton University Press.
  4. Taylor, J. W., Hann-Soden, C., Branco, S., Sylvain, I., & Ellison, C. E. (2015). Clonal reproduction in fungi. Proceedings of the National Academy of Sciences, 112(29), 8901-8908.
  5. Viegas, J., & Baum, M. (2016). Fungi and Molds. The Rosen Publishing Group, Inc.

Yet No Comments