Mating in fungi - Wikipedia
Such fungi require the presence of thalli of different mating types in order for the tips of opposite mating aerial hyphae, causing the hyphae to grow toward. Section 21–1. This section describes the defining characteristics of fungi. How thick is each hypha? Each hypha When the hyphae of opposite mating types meet, their two gametangia join, and the haploid nuclei contained in them fuse to. When hyphae from opposite mating types meet, they produce structures called progametangia that are dense and multinucleate. Cell walls form to separate the .
Fungi employ a variety of methods to bring together two compatible haploid nuclei plasmogamy. Some produce specialized sex cells gametes that are released from differentiated sex organs called gametangia.
In other fungi two gametangia come in contact, and nuclei pass from the male gametangium into the female, thus assuming the function of gametes. In still other fungi the gametangia themselves may fuse in order to bring their nuclei together. Finally, some of the most advanced fungi produce no gametangia at all; the somatic vegetative hyphae take over the sexual function, come in contact, fuse, and exchange nuclei.
Fungi in which a single individual bears both male and female gametangia are hermaphroditic fungi. Rarely, gametangia of different sexes are produced by separate individuals, one a male, the other a female. Such species are termed dioecious. Dioecious species usually produce sex organs only in the presence of an individual of the opposite sex. Sexual incompatibility Many of the simpler fungi produce differentiated male and female organs on the same thallus but do not undergo self-fertilization because their sex organs are incompatible.
Such fungi require the presence of thalli of different mating types in order for sexual fusion to take place. Gametes produced by one type of thallus are compatible only with gametes produced by the other type.
Such fungi are said to be heterothallic.
Many fungi, however, are homothallic; i. Some of the most complex fungi e. Homothallism and heterothallism are encountered in fungi that have not developed differentiated sex organs, as well as in fungi in which sex organs are easily distinguishable. Compatibility therefore refers to a physiological differentiation, and sex refers to a morphological structural one; the two phenomena, although related, are not synonymous.
Sexual pheromones The formation of sex organs in fungi is often induced by specific organic substances. Although called sex hormones when first discovered, these organic substances are actually sex pheromoneschemicals produced by one partner to elicit a sexual response in the other. In Allomyces order Blastocladiales a pheromone named sirenin, secreted by the female gametes, attracts the male gametes, which swim toward the former and fuse with them.
The nuclei join in a process called karyogamy to form a zygote. Mating in Ascomycota[ edit ] As it approaches a mate, a haploid sac fungus develops one of two complementary organs, a "female" ascogonium or a "male" antheridium. These organs resemble gametangia except that they contain only nuclei. A bridge, the trichogyne forms, that provides a passage for nuclei to travel from the antheridium to the ascogonium.
A dikaryote grows from the ascogonium, and karyogamy occurs in the fruiting body. Neurospora crassa[ edit ] Neurospora crassa life cycle. The haploid mycelium reproduces asexually by two processes: In the sexual cycle, mating can only occur between individual strains of different mating type, A and a. Fertilization occurs by the passage of nuclei of conidia or mycelium of one mating type into the protoperithecia of the opposite mating type through the trichogyne.
Fusion of the nuclei of opposite mating types occurs within the protoperithecium to form a zygote 2N nucleus. Neurospora crassa is a type of red bread mold of the phylum Ascomycota. Analysis of genetic recombination is facilitated by the ordered arrangement of the products of meiosis within a sac-like structure called an ascus pl. In its natural environment, N. It often can be found growing on dead plant matter after fires.
The results of these experiments led directly to the "one gene, one enzyme" hypothesis that specific genes code for specific proteins. This concept launched molecular biology.
Like other Ascomycetes, N. There is no evident morphological difference between the A and a mating type strains. Both can form abundant protoperithecia, the female reproductive structure see Figure.
Mating in fungi
Protoperithecia are formed most readily in the laboratory when growth occurs on solid agar synthetic medium with a relatively low source of nitrogen.
A branched system of slender hyphae, called the trichogyne, extends from the tip of the ascogonium projecting beyond the sheathing hyphae into the air.
The sexual cycle is initiated i. Such contact can be followed by cell fusion leading to one or more nuclei from the fertilizing cell migrating down the trichogyne into the ascogonium. Since both A and a strains have the same sexual structures, neither strain can be regarded as exclusively male or female. However, as a recipient, the protoperithecium of both the A and a strains can be thought of as the female structure, and the fertilizing conidium can be thought of as the male participant.
The subsequent steps following fusion of A and a haploid cells have been outlined by Fincham and Day. Instead, a nucleus from the fertilizing cell and a nucleus from the ascogonium become associated and begin to divide synchronously.
Fungus - Sexual reproduction | francinebavay.info
The products of these nuclear divisions still in pairs of unlike mating type, i. Each of these ascogenous hyphae bends to form a hook or crozier at its tip and the A and a pair of haploid nuclei within the crozier divide synchronously.
Next, septa form to divide the crozier into three cells. The central cell in the curve of the hook contains one A and one a nucleus see Figure.
Next the two uninucleate cells on either side of the first ascus-forming cell fuse with each other to form a binucleate cell that can grow to form a further crozier that can then form its own ascus-initial cell. This process can then be repeated multiple times. After formation of the ascus-initial cell, the A and a nuclei fuse with each other to form a diploid nucleus see Figure.
This nucleus is the only diploid nucleus in the entire life cycle of N. The diploid nucleus has 14 chromosomes formed from the two fused haploid nuclei that had 7 chromosomes each. Formation of the diploid nucleus is immediately followed by meiosis. The two sequential divisions of meiosis lead to four haploid nuclei, two of the A mating type and two of the a mating type. One further mitotic division leads to four A and four a nucleus in each ascus.
Meiosis is an essential part of the life cycle of all sexually reproducing organisms, and in its main features, meiosis in N. As the above events are occurring, the mycelial sheath that had enveloped the ascogonium develops as the wall of the perithecium becomes impregnated with melanin, and blackens.
The mature perithecium has a flask-shaped structure. A mature perithecium may contain as many as asci, each derived from identical fusion diploid nuclei. Ordinarily, in nature, when the perithecia mature the ascospores are ejected rather violently into the air. For normal strains, the entire sexual cycle takes 10 to 15 days.