Hi, my name is Stephen Mayfield. I'm professor of Biology at UC San Diego, and director of the California Center for Algae Biotechnology. And today, we're going to talk about green algae. So, why are they green algae? Well, the simplest explanation is that they contain chlorophyll A and B as their primary pigments, and that makes them green colored. So, quite literally, they are green colored algae. They come from a division of algae called the Chlorophytes and the Charophytes. And this is also the division that higher plants come from. So, as we'll show you in just a minute, green algae and higher plants are very closely related. They mainly are found in freshwater, although, of course, like everything, there's always some exception to that rule. And there are a set of Ulvophyceae, which are marine green algae. They're quite often unicellular, but multicellular green algae are possible. And all of them have chloroplast, and that's a fundamental function, a fundamental structure of green algae. And we'll talk about that in a little bit too. So, as I said, green algae are just one branch of algae. Here on this diagram it's shown in the lower right hand corner. But there are still pretty diverse set of algae that come out of that. What's shown in the phylogenetic tree to the right, shows the chlorophytes and the charophytes, and then it shows the plant lineage coming off those in the bottom. And although it's a little hard to see in this slide, the very bottom of that figure shows the time that these things have been separated. And if you look really closely on that, you'll see that even within the green algae lineage, many of these species have been separated for hundreds of millions, or even a billion years. And what does that separation mean? That separation means that with time comes genetic diversity, and with genetic diversity comes physiological diversity. So, the green algae, even though they all share pigments the same, they're pretty different on their secondary metabolites. We'll talk a little bit about that too. So, this is a picture of a green algae cell. And a couple of the important things you'll see in it like all algae, this is a eukaryote. So, you have a nucleus, and the nucleus by far contains most of the genetic material inside the cell, 99 percent of the genetic material is contained within that cell. They also have mitochondria, and here in this slide it's shown as a little circular mitochondria. This is quite often what you see in textbooks, I'll show you in a minute. They don't always look like that inside of a real cell, but in this diagram they have mitochondria. They also have a very large chloroplast. It'll take up to 60 percent of the cell structure, because, after all, one of the most important functions that all algae do is carry on photosynthesis. So, that's always a major component of the cell. This happens to be a picture of a green algae Chlamidomonas reinhardii. That is a motile algae, so there are two flagella, so it's capable to swim around. It has something called a pyrenoid, that contains the carbon fixing enzyme, RuBisCO. And then it also has a cell wall, and assorted other vacuoles. As I said, although that's what a cartoon diagram of it looks like, here's a fluorescent image of some of those subcellular structures. And here what we've done, is we've taken fluorescent proteins and targeted them to those different subcellular structures. So, here we put mCherry, or a bright red fluorescent protein, into the endoplasmic reticulum. We put a Cerulean, which is a blue protein, into the nucleus. And we put a green protein called Venus into the mitochondria. And those are individual cells, each expressing those, and those are live cell images. So, you can see those beautiful red, blue, and green colors. And then, if we cross all of those together, we can get the single cell showed on the right. And I think in that when you get a really good idea of just how dynamic these structures are. So, the mitochondria, in fact, are not little round vesicles floating around. They're quite a dynamic structure, and this is also true of the endoplasmic reticulum, and even the the nucleus. Okay, as I said, green algae and plants come from the same lineage. And, in fact, if you look at their photosynthetic complexes, what you will see is they are almost identical. In fact, one of the reasons that we studied green algae for many many years is because the photosynthetic complexes were identical between green algae and terrestrial crop plants that we use to produce food. So, there was a great deal of interest, because we could do genetics so much quicker in algae, to look at it in this system. And this is simply a cartoon, where we've highlighted each of the individual proteins, that are found in those complexes. If you were to look at the photosynthetic apparatus from a brown algae, or a red algae, or even a cyanobacteria, you would certainly see similarities. They all have photosystem two, they all have a cytochrome complex, they all have photosystem one, they all have ATP, and the carboxylates complex. So, they have the same big complexes, but the protein structures are very different, and the amino acid sequence is very different in those other algae. But between higher plants and algae, very similar, as you see here in this cartoon. And we've taken advantage of that for lots of studies in these organisms. So, as I said, green algae, their genomes are quite well understood. So, there's three genomes. There's a chloroplast genome, and that's a small circular genome, we'll talk about that in another class. There's a nuclear genome that has chromosomes much larger, almost 100 times larger than the chloroplast genome. And then there's a mitochondrial genome. And the mitochondrial genomes actually vary greatly. In some algae, the mitochondrial genomes are as small as 15 kilobases, and in other algae they can be upwards of 600 to 700 kilobases. Importantly, in several green algae all three of those genomes are transformable. And in the chloroplast and nucleus, we actually have very good genetic tools, and we can take advantage of that. And we'll talk about that in several other classes as we go on. Finally, as I said, green algae genomes have significant homology with other algal genomes, but most of that is in the photosynthetic apparatus. So, what this diagram shows here, it's a little hard to see, but what that shows is every place where the circles overlap, that's where they have genes that are homologous to each other. So, if you look at this, the brown algae and the green algae, they actually only share about 40 percent of their genomes in common. So, what does that mean? That means 40 percent of the proteins we can identify that must have similar function. The red algae, about the same. So, what this shows is that there is good homology between the core set of genes, but then a great diversity once you get outside of that. And with that, I said, with that genetic diversity also comes physiological diversity. And that's one of the things that we will take advantage of in algae when we want to produce a lot of different compounds in them. And, finally, why do we care about green algae? Well, we care about green algae, because several of them are already used as food today. This is just a picture of two. One is Chlorella. This is a small green algae, very, very fast growing, and it's found in a lot of different foods today. You might see it in the store, in fact, if you buy something called Green Machine or Super Green, some of these sort of health food drinks, they quite often have chlorella, and then a cyanobacteria called spirulina in it. And then shown on the right, this is a new product, it's out from a company called TerraVia. So, they grow a chlorella, and they extract from that, the oil out of it, the triglycerides out of that, and they sell that as cooking oil. And it's a very high quality cooking oil, so it can go to a very high temperature, and it doesn't impart a lot of flavor to the food. And that turns out to be important for a lot of different things you cook. So, one of the reasons that we study green algae, and one of the reasons that they're going to become more important in the future is that they're a very good source of food.
