WEBVTT 1 00:00:05.410 --> 00:00:12.011 Welcome to the chapter dedicated to two models of brown algae: Saccharina and Ectocarpus. 2 00:00:12.211 --> 00:00:18.112 These two brown algae belong to different orders, Ectocarpus belongs to Ectocarpales 3 00:00:18.312 --> 00:00:22.457 which usually includes very simple algae with very simple morphology, 4 00:00:22.757 --> 00:00:29.468 usually filamentous, while Saccharina belongs to Laminariales, which includes 5 00:00:29.688 --> 00:00:34.632 much larger algae - we call them kelp. Saccharina and Ectocarpus are close 6 00:00:34.932 --> 00:00:41.910 phylogenetically. They diverged 75 mya. This duration might look or sound long to 7 00:00:42.110 --> 00:00:47.320 you, but actually this is the same that separates humans from rodents like mice. 8 00:00:48.530 --> 00:00:53.837 So let's see if Saccharina and Ectocarpus are as different as humans and rodents. 9 00:00:54.137 --> 00:00:56.007 Let's start with Ectocarpus. 10 00:00:56.790 --> 00:01:02.416 Ectocarpus was first described as Conferva siliculosa by Dillwyn at the beginning of the 11 00:01:02.616 --> 00:01:09.566 19th century. It is a tiny, filamentous alga found in temperate waters in both northern 12 00:01:09.866 --> 00:01:12.056 and southern hemispheres. 13 00:01:12.350 --> 00:01:16.623 This wide distribution is not common in brown algae, and this might be due to 14 00:01:16.923 --> 00:01:21.235 the fact that this alga sticks easily to any surface. 15 00:01:21.500 --> 00:01:27.560 It is a widespread biofouling agent, an issue for boats and marine equipment in general. 16 00:01:28.130 --> 00:01:34.285 Let's see how it develops and reproduces. Actually, Ectocarpus develops two generations 17 00:01:34.585 --> 00:01:40.189 which alternate within the life cycles, and this is very common in macroalgae. 18 00:01:40.489 --> 00:01:46.029 The 1st generation is a sporophyte and it is diploid. It is made of a string of cells 19 00:01:46.229 --> 00:01:52.840 like pearls in a necklace. It grows apically, and reaching a given stage, it branches. 20 00:01:53.720 --> 00:01:57.541 All the filaments produced then are similar to the initial filament. 21 00:01:57.741 --> 00:02:00.647 This is a re-iterative development.  22 00:02:01.386 --> 00:02:07.328 This produces a prostrate base sticking to a solid suface. After about four weeks, the 23 00:02:07.528 --> 00:02:11.245 sporophyte resemble a tuft of about one centimeter wide, 24 00:02:11.545 --> 00:02:14.160 made of many filaments attached to each other. 25 00:02:15.220 --> 00:02:19.335 They can all undulate in the seawater because only their base is attached. 26 00:02:19.635 --> 00:02:24.739 After a few more days they will differentiate reproductive organs, named sporangia, 27 00:02:25.039 --> 00:02:27.940 which would produce meiospores. 28 00:02:29.110 --> 00:02:34.270 These meiospores are haploid, they are released in the seawater where they settle 29 00:02:34.570 --> 00:02:39.239 to the bottom. They will then germinate as haploid gametophytes. This is what is 30 00:02:39.539 --> 00:02:42.690 shown in the yellow part of the diagram. 31 00:02:43.600 --> 00:02:47.950 There are female and male meiospores, and they will each produce a distinct 32 00:02:48.150 --> 00:02:53.477 gametophyte. Gametophytes are also filamentous but they lack the basal part 33 00:02:53.777 --> 00:02:59.014 seen in the sporophyte so that they float more easily. They also produce reproductive 34 00:02:59.314 --> 00:03:05.494 organs, this time named gametangia because they are the ones producing the gametes. 35 00:03:05.794 --> 00:03:11.634 Male and female gametophytes look similar morphologically and it is stated that 36 00:03:11.834 --> 00:03:17.191 Ectocarpus has virtually no sexual dimorphism. Both types of gametes are 37 00:03:17.455 --> 00:03:22.851 also released freely in the sea water, where they will fuse together to produce the diploid 38 00:03:23.130 --> 00:03:30.061 sporophytes. The female gamete produces a pheromone, Ectocarpen, which attracts 39 00:03:30.361 --> 00:03:34.941 the male gametes. So to summarise about this life cycle, we call it a haplodiplontic 40 00:03:35.146 --> 00:03:39.687 life cycle because it has two generations, haploid and diploid. 41 00:03:39.987 --> 00:03:46.487 It is isomorphic because both the gametophyte and the sporophyte look similar. 42 00:03:46.739 --> 00:03:51.763 It is dioicous because the sexes are carried by two independent organisms, 43 00:03:52.063 --> 00:03:54.820 here the female and the male gametophytes. 44 00:03:55.100 --> 00:04:00.398 And finally it is isogamous because both gametes are similar. 45 00:04:00.698 --> 00:04:05.405 In nature this generation can be found at different locations and at different times, 46 00:04:05.705 --> 00:04:08.610 but it all depends on the species and the strain. 47 00:04:09.690 --> 00:04:14.466 And in the lab we usually work with a specific strain which is able to reproduce 48 00:04:14.766 --> 00:04:21.399 vegetatively, its unfertilised gametes are able to germinate and to produce a pattern 49 00:04:21.699 --> 00:04:27.386 of sporophytes and it's very convenient for example to produce mutants because it eases 50 00:04:27.686 --> 00:04:29.210 the screening of phenotypes. 51 00:04:29.910 --> 00:04:34.690 Ectocarpus has been a model for academic research for at least 15 years. 52 00:04:34.990 --> 00:04:39.256 In 2010 its genome has been sequenced. 53 00:04:39.556 --> 00:04:45.844 It is 214 mega base pairs, it has and codes for 17,000 genes. 54 00:04:47.180 --> 00:04:54.037 Its genome has a peculiar organisation, the genes are made of a given number of 55 00:04:54.337 --> 00:04:57.490 short exons and they are split by pretty large introns. 56 00:04:58.690 --> 00:05:02.822 Since, several technical tools have been developed and I will present some of them 57 00:05:03.122 --> 00:05:04.210 in the next chapter. 58 00:05:04.850 --> 00:05:08.454 Now we will shift to the second brown algal model, Saccharina. 59 00:05:08.754 --> 00:05:14.667 Saccharina is very different from Ectocarpus. It was first described by Linneus in the 60 00:05:14.967 --> 00:05:20.007 middle of the 18th century who thought it resembled Ulva, and Ulva is the alga 61 00:05:20.307 --> 00:05:25.166 responsible for green tides. So consequently he first named it 62 00:05:25.466 --> 00:05:30.849 Ulva latissima, but since, the name has changed several times, first Saccharina 63 00:05:31.149 --> 00:05:34.840 at the beginning of the 19 century, then 64 00:05:35.280 --> 00:05:41.671 Laminaria saccharina, and 200 years later, back to Saccharina latissima. 65 00:05:41.971 --> 00:05:44.231 In Asia it is just named kombu. 66 00:05:44.531 --> 00:05:49.941 The origin of Saccharina can be traced to the subarctic waters of the northern Pacific 67 00:05:50.241 --> 00:05:55.560 Ocean, then it dispersed to the northern Atlantic, but is still absent from the 68 00:05:55.860 --> 00:05:57.460 southern hemispheres. 69 00:05:58.180 --> 00:06:03.100 The life cycle of Saccharina has also two generations, but this time the two 70 00:06:03.400 --> 00:06:08.555 generations show large differences in size. The gametophyte is microscopic as in 71 00:06:08.855 --> 00:06:14.654 Ectocarpus, and the sporophyte is much bigger. Gametophytes usually live during 72 00:06:14.954 --> 00:06:20.253 summer and autumn, while the sporophyte develops during winter and spring. 73 00:06:20.780 --> 00:06:26.131 As in Ectocarpus, the life cycle is dioicous, meaning that the two sexes are carried by 74 00:06:26.331 --> 00:06:31.340 two independent organisms, here the haploid male and the haploid female gametophytes. 75 00:06:33.300 --> 00:06:39.193 However, in contrast to Ectocarpus, the gametophyte usually does not develop much. 76 00:06:39.420 --> 00:06:45.140 They are filamentous, but immediately get fertile so that they don't have time to expand. 77 00:06:46.330 --> 00:06:52.949 Also in contrast to Ectocarpus, the female gametophyte produces eggs, rather big, 78 00:06:53.249 --> 00:06:55.990 which remain attached to the maternal tissue. 79 00:06:57.150 --> 00:06:59.540 The sperm cells have to swim to the egg. 80 00:07:00.790 --> 00:07:04.393 As a result, the embryo remains attached to the maternal tissue. 81 00:07:04.793 --> 00:07:11.140 Therefore, this life cycle, as in Ectocarpus, is haplodiplontic and dioicous. 82 00:07:11.940 --> 00:07:17.216 But in contrast to Ectocarpus, it is hetero- morphic because the sporophyte looks 83 00:07:17.516 --> 00:07:23.866 different from the gametophyte, and it is oogamous because the female gametophyte 84 00:07:24.166 --> 00:07:27.794 produces an egg and the male gametophyte a sperm cell. 85 00:07:28.073 --> 00:07:32.615 The genome of Saccharina japonica has been sequenced since 2015. 86 00:07:33.415 --> 00:07:40.407 It is three times larger than that of Ecto- carpus with 518 mbp and twice more genes. 87 00:07:41.740 --> 00:07:46.100 When scientists analysed the genome structure, they found that several gene 88 00:07:46.400 --> 00:07:52.380 families expanded. The first one is the one involved in the metabolism of iodine, 89 00:07:52.680 --> 00:07:57.725 and this fits very well with the biology of Saccharina, which is the most efficient 90 00:07:58.025 --> 00:08:01.600 accumulator of iodine within all the living systems. 91 00:08:02.190 --> 00:08:08.500 They are capable of pumping up to 30k-fold the concentration of iodine in the seawater. 92 00:08:09.380 --> 00:08:13.540 Consequently, they accumulate up to 1% of their dry weight. 93 00:08:15.600 --> 00:08:19.804 The second gene family, which expanded in the genome of Saccharina is that 94 00:08:20.004 --> 00:08:24.185 involved in the biosynthesis of alginate, which is this polysaccharide present in 95 00:08:24.485 --> 00:08:28.246 the cell wall, and this fits again very well with the biology of this alga, 96 00:08:28.446 --> 00:08:33.795 which is a high producer of alginate. Up to 34% of its dry weight. 97 00:08:33.995 --> 00:08:39.045 So now I hope you have a better idea of what Ectocarpus and Saccharina are 98 00:08:39.245 --> 00:08:45.029 and how they differ in many aspects. In chapter one, you saw how Saccharina 99 00:08:45.329 --> 00:08:46.740 is cultivated in the sea. 100 00:08:47.040 --> 00:08:53.409 In Chapter 4 you will see how it is cultivated in the lab to address research topics 101 00:08:53.609 --> 00:08:55.550 that you will hear about in Chapter 5.