Fungi Reproduction - Online Tutor, Practice Problems & Exam Prep

Fungi reproduce through sexual and asexual methods, primarily using spores produced in structures called fruiting bodies. Sexual reproduction involves plasmogamy, where hyphae fuse, forming a dikaryotic cell with two genetically distinct nuclei, followed by karyogamy, resulting in a diploid zygote. Zygomycetes form zygosporangia, while Basidiomycota and Ascomycota produce basidiocarps and ascocarps, respectively, with distinct spore-producing cells. Chytrids uniquely exhibit alternation of generations with flagellated spores called zoospores. Understanding these processes is crucial for grasping fungal biology and ecology.

Fungi Reproduction - 1

Hi. In this video, we're going to talk about how fungi reproduce. Fungi show both sexual and asexual reproduction. However, there are some fungi that only reproduce asexually, and we call those deuteromycetes. It's worth noting that all fungi will reproduce using spores, regardless of whether it's sexual reproduction, asexual reproduction, or whatever. The spore-producing structures that fungi create are usually called fruiting bodies, kind of an informal name for them. As you'll see, there are more technical terms for types of fruiting bodies, and we'll cover those as we go on. Fungi don't fall into the traditional male-female dichotomy like many other organisms we've talked about. Fungi do have mating types, but the different mating types don't actually appear morphologically different. So, you're probably wondering, how do fungi know who to mate with? The answer is they use pheromones to communicate their mating type, and these are secreted chemical signals that the fungi will secrete and other fungi will pick up on and say, 'hey, you're looking pretty good tonight.' If you're curious about learning a little more about these chemical signals and fungal mating, if you check out the chemical signals chapter, you can learn a little bit about yeast mating.

Now, before we move on, I do want to say that part of the reason we don't use a simple male-female dichotomy when talking about fungi mating types is that they have so many different mating types within a single species. In fact, some species actually can have 1,000 of different mating types. This is why the old male-female breakdown just doesn't cut it. Fertilization will occur by hyphae fusing together, and then eventually their nuclei fusing together. This is going to be something, a trend you're going to see in all the types of fungi we're going to talk about except for the chytrids. They actually do it a little differently. We'll get to that later. But first, let me give you a general overview of what a fungal life cycle might look like. This is not specific, this is just general. The first stage of sexual reproduction, if you want to think of it in stages, is going to be the fusion of hyphae. You see that happening here. We call that plasmogamy. And essentially, it's when the cytoplasm of two cells fuse. But the nuclei don't fuse yet. We don't have fusion of nuclei. That actually has its own special name. So the resulting cell is going to be considered heterokaryotic. And that's because it's going to have two, it can have two or more technically, but let's just say two for now, nuclei that are genetically different from one another. In the case of our example of fungus, these are going to be two haploid nuclei that are genetically distinct. It can be more than two nuclei, just to be clear about that. Heterokaryotic can refer to something that has two or more genetically distinct nuclei. And in our example, I'm just going to leave it at two nuclei to keep things simple. And so you'll often see this written as n + n. Now remember n usually means haploid. But because our fungus is going to have two haploid nuclei together in a cell, we sometimes see it written as n+n.

In our example, we're talking about a cell that is dikaryotic, meaning it contains two nuclei. Right? So, dikaryotic means it has two nuclei. Heterokaryotic means it has two or more genetically distinct nuclei. Right? Karyo is going to refer to the nucleus. And Hetero means different. Di means two. That's where these terms come from. Now, the final stage of sexual reproduction is going to be when those two haploid nuclei fuse and form a zygote. We call this karyogamy, and you can see that happening right here. Here we have our technically, here we're actually seeing plasmogamy and karyogamy. So let me be clear about that. We have first plasmogamy. And then here, this first portion is plasmogamy, and then this second portion is karyogamy. And that is the fusion of the two nuclei into one new, now diploid, nucleus. This is going to form the zygote. The zygote will form a spore-producing structure. Right? Fruiting body, if you will. And in most fungi, the zygote is actually the only diploid stage of the fungus. And that's why we don't really have a good picture of it in this nice little drawing of a fungal life cycle because it's often just a transient single-celled structure. Now, this fruiting body that you see here, you might recognize as a mushroom. Yes. In fact, mushrooms are the fruiting bodies of various fungi. So when we talk about fungi, we're actually usually talking about the reproductive structures, not the main fungal body, the mycelium. So, this fruiting body develops. It's going to give off its spores. Right here, we have spores, and these spores are going to disperse and what this image is trying to depict is being dispersed through rain, through insects. That's more in the realm of ecology. We'll talk about dispersal in a different chapter. The main point is these spores are going to eventually germinate, form hyphae, that's what these are, these are hyphae, and then the process will repeat. Two hyphae of different mating types—that's what these two colors are supposed to represent, mating types. So these two hyphae of different mating types will get together again. Fuse hyphae, plasmogamy, karyogamy, zygote leads to spore-producing structure, which releases spores. Right? The fruiting body releases spores, those spores germinate, more hyphae, and on and on and on.

Now, I did say there was an exception to this cycle, and that comes in the form of the chytrids, which are actually the only fungi to exhibit alteration of generations. Remember, alteration of generations is when you have a multicellular sporophyte generation and gametophyte generation. Similar to plants, and some protists for that matter. What distinguishes the chytrids are their flagellated spores and gametes. And we actually have a special term for these flagellated spores; we call them zoospores. These are again produced by chytrids, which are fungi that do not follow the model of reproduction that we just went through. Alright, with that, let's flip the page and take a look at some specifics.

Fungi Reproduction - 2

Now zygomycetes are named for their distinctive reproductive structure, the zygosporangium, and this is what's formed after plasmogamy. So you'll notice, here we have our plasmogamy stage, 2 hyphae are going to get together and they're going to fuse and form a zygote after karyogamy. Right? So, first, they'll fuse, cytoplasm, then the nuclei will fuse, will form a zygote at that point. And the zygote is gonna develop into the zygosporangia, which is the spore-producing structure of a zygomycete that arises from the fusion of hyphae. And actually, very cool, it sits as kind of this blob. So here we have our zygosporangium. Right. Again, sporangium, that's gonna be the singular form of this word. So our zygosporangia, right here, this structure, and, essentially, this is going to sprout, spore-producing structure that you can see right here and the structure will rupture, giving off the various spores. And those spores will then, eventually turn in germinate, turn into hyphae, and grow and, you know, get together and repeat the cycle. So this is the sexual zygomycetes but it's worth noting that they actually have an asexual form of reproduction where these sporangiophores form from their hyphae and, basically their stalks with sporangia at the tip. So a structure not unlike this one we saw here. Of course, these are going to release spores that were created through asexual reproduction though, not sexual reproduction. And again, those asexual spore-producing structures are called sporangiophores, not sporangiophores. Alright. Moving on, we have Basidiomycota and these are mushrooms that we're familiar with eating. Though actually, as you'll see, not all mushrooms that we eat are basidiomycota.

Now, basidiomycota have reproductive structures that are made of dikaryotic hyphae, and again, these are mushrooms. And these dikaryotic hyphae have what are called basidia on their end. So looking at our diagram here, the fruiting body is also called the basidiocarp. You can see it right there. It kind of looks like a cross-section, like if you cut a mushroom in half, but basically, basidiocarps are mushrooms that we're used to seeing. Like, if you were to draw a cartoon of a mushroom, you'd be drawing a basidiocarp. So these basidiocarps are, again, made up of these dikaryotic hyphae and on their tips which, if we're looking at this mushroom here, basically hanging, on the underside of the mushroom are these basidia or basidium, singular. And these are the spore-producing cells in which karyogamy is gonna occur. And they're going to produce basidiospores, which go on to germinate, form hyphae. And, you know, those hyphae of different mating types will get together, plasmogamy. The dikaryotic hyphae will then form, mushroom, a basidiocarp, and the process will repeat itself. And, it's these basidia, these spore-producing structures, that give this group of fungi its name.

Fungi Reproduction - 3

Ascomycota have reproductive structures that are made of dikaryotic hyphae, but unlike Basidiomycota, they form asci on their ends, not basidia. Now, asci are spore-producing structures, and they specifically produce 8 haploid spores, called ascospores, and these asci, that is, are contained within an ascocarp, which is the fruiting body of Ascomycota. And you might recall from the first video on fungi that we looked at a morel mushroom. Well, that's an example of an ascocarp. So, the basidiocarps and ascocarps are the mushrooms that we're normally eating when we eat mushrooms. And again, those are the reproductive structures of fungi, not the main fungal body, the mycelium.

Now, looking at Ascomycota reproduction, we actually will form the ascus. You can see the initial ascus there. We have the 2 cells, they'll fuse to form the zygote, and then we'll have a series of cell divisions. You don't really need to worry about the specifics of all of that, but through a series of cell divisions, we go from having a diploid zygote to 8 haploid spores. You can see those all here, and they are contained in the ascus sac. And the ascus itself really is kind of like a sac, and that's why these are sometimes called sac fungi. And what's kind of crazy about these ascus sacs is when the spores are ready to go, these ascus sacs, which unlike basidia, remember basidia hang down there on the external surface of the basidiocarp. These asci are actually inside the ascocarp and these spores will be forcibly ejected from this sac. So, they burst forth and are spread that way. And of course, the ascospores will germinate, turn into hyphae. And these hyphae can actually also reproduce asexually. And when they reproduce asexually, they form spores called conidia. And what's interesting is these conidia, as you can see happening here and here, these conidia can actually also be involved in sexual reproduction. So, they can fertilize another fungus of a different mating type, or they can germinate and turn into hyphae in an asexual reproductive process.

Alright. That's all I have for fungal reproduction. I'll see you guys next time.

Here’s what students ask on this topic:

How do fungi reproduce sexually?

Fungi reproduce sexually through a process involving two main stages: plasmogamy and karyogamy. In plasmogamy, the cytoplasm of two hyphae from different mating types fuse, forming a dikaryotic cell with two distinct haploid nuclei. This stage is followed by karyogamy, where the haploid nuclei fuse to form a diploid zygote. The zygote then undergoes meiosis to produce haploid spores, which are released from structures called fruiting bodies. These spores germinate to form new hyphae, continuing the life cycle. This process ensures genetic diversity in fungal populations.

What are the differences between Basidiomycota and Ascomycota reproductive structures?

Basidiomycota and Ascomycota have distinct reproductive structures. Basidiomycota produce basidiocarps, commonly known as mushrooms, which contain basidia on their gills. Basidia are spore-producing cells where karyogamy occurs, leading to the formation of basidiospores. In contrast, Ascomycota form asci within ascocarps. Asci are sac-like structures that produce eight haploid ascospores through meiosis. These ascospores are forcibly ejected from the asci. Both groups have dikaryotic hyphae, but their spore-producing structures and mechanisms differ significantly.

What is plasmogamy in fungi?

Plasmogamy is the initial stage of sexual reproduction in fungi, where the cytoplasm of two hyphae from different mating types fuse. This fusion results in a dikaryotic cell, which contains two genetically distinct haploid nuclei. Plasmogamy precedes karyogamy, the fusion of the nuclei, and is crucial for the formation of the dikaryotic stage in the fungal life cycle. This process allows for genetic recombination and diversity in fungal populations.

What are chytrids and how do they reproduce?

Chytrids are a unique group of fungi that exhibit alternation of generations, similar to plants. They have both a multicellular sporophyte and gametophyte generation. Chytrids reproduce using flagellated spores called zoospores, which can swim in water. These zoospores are produced in sporangia during the sporophyte stage. The gametophyte stage produces gametes, which also have flagella. Fertilization occurs when these gametes fuse, forming a new sporophyte. This reproductive strategy distinguishes chytrids from other fungi.

What are deuteromycetes and how do they reproduce?

Deuteromycetes, also known as imperfect fungi, are fungi that reproduce only asexually. They do not have a known sexual reproduction stage. Deuteromycetes produce asexual spores called conidia, which are formed on specialized hyphae called conidiophores. These spores are dispersed and germinate to form new hyphae, continuing the asexual life cycle. The lack of sexual reproduction in deuteromycetes means they do not undergo genetic recombination, relying solely on mutations for genetic variation.