Marker Genes

Grace Troupe, Presenter Author

10/11/2018 Added

1205 Plays

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When Agrobacterium is used to insert a transgene into a plant, one or two extra genes can be added to help simplify the transformation process. These are known as marker genes. For a basic idea of why and how marker genes are used, watch this video.

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[00:00:05.471]In the last video, we learned
[00:00:07.517]how you can get this new segment of DNA
[00:00:10.930]into a plasmid so that way an agrobacterium
[00:00:15.110]can use that to deliver the transgene into a new plant.
[00:00:19.790]But, what we didn't tell you is
[00:00:21.050]what all's included in this region of DNA
[00:00:23.488]that the agrobacterium sends over.
[00:00:27.160]So, let's take a closer look
[00:00:28.840]at what they included in this specific story.
[00:00:33.180]So, what did the region of DNA contain
[00:00:35.310]that we put in the plasmid?
[00:00:38.380]So, there's three different regions,
[00:00:40.210]the first one, comes as no surprise,
[00:00:42.460]our main goal is to get the transgene into the new plant
[00:00:45.139]and so we have our transgene with that soybean promoter
[00:00:48.654]and the Arabidopsis coating region,
[00:00:52.590]then these next two are regions
[00:00:54.151]that just help make the plant transformation process easier.
[00:00:59.650]So these are called marker genes.
[00:01:01.280]This first one is an antibiotic resistance marker gene.
[00:01:05.706]And the second one is a herbicide resistance marker gene.
[00:01:08.920]And these genes help distinguish between
[00:01:12.600]plants that did get the gene
[00:01:14.070]and plants that did not get the new gene,
[00:01:16.140]or this new segment of DNA.
[00:01:18.060]'Cause this will all get passed
[00:01:19.220]into the plant together, as one unit.
[00:01:23.704]So, first let's take a look
[00:01:25.150]at how this antibiotic resistance marker gene
[00:01:28.480]helps us distinguish between transgenic and non-transgenic.
[00:01:32.390]So, this gel that these leaves are growing in,
[00:01:36.140]it has hormones that cause the cells of these leaves
[00:01:41.170]to start producing shoots,
[00:01:43.160]to start growing new shoots.
[00:01:44.860]But it also has an antibiotic that kills plant cells.
[00:01:49.630]So, these new shoots can only grow
[00:01:52.170]from cells that got the antibiotic resistance gene.
[00:01:56.260]So, if they inherited that gene,
[00:01:57.880]that means they probably got that entire segment of DNA
[00:02:00.380]which includes the transgene.
[00:02:02.022]So, what this first marker gene does,
[00:02:04.633]is it, tries to make it so only,
[00:02:08.147]shoots only grow if they have the new gene.
[00:02:11.593]This helps reduce the number of plants
[00:02:14.580]that you're working with,
[00:02:15.947]otherwise every cell in this leaf could produce a new shoot,
[00:02:19.720]theoretically and you'd have thousands of plants
[00:02:22.320]but only some of them would have a gene.
[00:02:24.534]Where this way, most all of the ones growing
[00:02:27.023]have the new gene.
[00:02:30.242]Alright, so, we have a second marker gene in this story,
[00:02:33.972]and this one is kind of a way to double check.
[00:02:37.230]'Cause every once in a while you get a plant
[00:02:39.690]that makes it through that gel medium,
[00:02:41.387]even though it didn't inherit the transgene.
[00:02:45.013]So, the second marker was herbicide resistance.
[00:02:48.259]Which, herbicides kill plants.
[00:02:51.600]So if, Shirley, the scientist
[00:02:54.210]striped herbicide across on those black lines on each plant,
[00:02:58.300]which one do you think got the transgene?
[00:03:03.096]I would say this one on the left, right,
[00:03:05.700]because it's not showing that it is reacting
[00:03:08.310]to the herbicide, which means
[00:03:09.860]it must have resistance.
[00:03:11.590]So, if it got that set of DNA with the three genes on it,
[00:03:14.851]that means that this one probably has the transgene,
[00:03:18.260]and this one on the right probably doesn't.
[00:03:23.120]So we use marker genes to help eliminate
[00:03:25.220]plants that don't have the transgene
[00:03:27.050]because it's not beneficial
[00:03:28.250]for us to keep working with a plant
[00:03:29.514]if it doesn't have the transgene in it.
[00:03:32.588]So this reduces the number of plants
[00:03:34.890]that we need to work with
[00:03:36.250]and thus reduces the cost.
[00:03:38.275]So let's take one more look at our regions.
[00:03:40.852]We included the transgene,
[00:03:43.070]which is what we want, ultimately,
[00:03:45.120]but these two marker genes
[00:03:46.410]helped us primarily work with plants that had the transgene.
[00:03:50.997]Even though we weren't testing the DNA
[00:03:53.380]we could tell because they had these other
[00:03:55.470]resistance genes that helped us screen plants.
[00:03:58.954]So, if you watch the next video, you can see
[00:04:00.761]how Shirley uses this with soybeans
[00:04:03.071]to fight sudden death syndrome.

Marker Genes

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Marker Genes

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