Fragrant Signal 1

Scott Dworak Author

02/12/2019 Added

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Fragrant Signals (4 minutes) describes the production of jasmonic acid in jar1 mutants and wild-type Arabidopsis thaliana, which led to the formation of a hypothesis and experiment.

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[00:00:00.000]Plants on our planet have amazing variation, but the one thing they all have in common
[00:00:07.000]is that they cannot run to avoid problems. One problem they often encounter during their
[00:00:13.380]life is insects that are herbivores. These animals use the plant as food, which can cause
[00:00:18.520]obvious problems for the plant. Plants do not just give up. They have a variety of genetically
[00:00:24.400]controlled defense mechanisms that plant biologists, such as Paul Staswick at the University of
[00:00:29.320]Nebraska, would like to better understand. The genetic response that plants can use to protect
[00:00:34.900]themselves from aggressive insect herbivores is complex and involves hormones. The Staswick lab
[00:00:40.600]at UNL is focused on the plant hormone, jasmonic acid. This hormone is known to stimulate the
[00:00:46.600]expression of genes involved in protecting plants. So we used a plant called Arabidopsis thaliana.
[00:00:52.600]Most people call it Arabidopsis. It's been the model plant of choice. It was the first plant
[00:00:58.640]that had its entire genome sequenced. Back in 2000 it was finished. And it was selected because
[00:01:04.100]there's relatively few genes. There's only about 25,000 compared to something like corn,
[00:01:09.620]has about 50,000. And it's a relatively small plant. It grows six weeks, can grow to reproduce.
[00:01:16.460]One plant can make about 5,000 seed. You can grow it, you know, in a lab, in a growth chamber and
[00:01:22.040]can grow a whole bunch in a small space. So jar1 is a mutant of Arabidopsis plant that
[00:01:27.960]essentially just has a mutation in one gene, the jar1 gene, that otherwise separates it from
[00:01:36.120]normal wild-type plants. It's the only difference it has this mutation in just this one gene but
[00:01:41.940]otherwise looks, you know, the same as a normal wild-type plant and you wouldn't be able to tell
[00:01:46.540]the difference just looking at them. So what Paul knew was this gene codes for this jar1 enzyme
[00:01:54.120]and what this enzyme does is it joins
[00:01:57.280]the hormone jasmonic acid with an amino acid, isoleucine,
[00:02:03.840]And the enzyme joins them, yielding this one compound called JA-isoleucine, or jasminoyl isoleucine.
[00:02:11.220]And for years, it was thought that regular jasmonic acid was the active hormone involved in responses.
[00:02:19.600]But Paul determined, no, it's this JA-isoleucine that is actually causing signaling responses.
[00:02:28.360]Since we had the wild-type and the mutant, the jar1s, these jar1 mutants were, whenever they were wounded mechanically,
[00:02:36.580]like with scissors or like a pair of pliers or something, these JA-isoleucine levels would peak within an hour of being wounded.
[00:02:46.900]But in the jar1 mutant, yeah, they would peak, but they were significantly reduced, like tenfold less than these wild-type plants.
[00:02:54.800]So knowing that, we hypothesized, well,
[00:02:58.220]what happens to insects feeding on them?
[00:03:00.520]Would it kind of go through the same pathway?
[00:03:03.040]Would this JA-isoleucine also peak in response to insects wounding?
[00:03:08.080]And of course, in the kar1 mutants, peak, you know, maybe tenfold less.
[00:03:12.340]We wanted to see ultimately if that jar1 enzyme is also active with insect feeding as it was with mechanical wounding.
[00:03:20.760]It was important for the UNL scientists to set up an experiment
[00:03:24.800]that would provide a fair test for their hypothesis.
[00:03:27.300]They needed
[00:03:28.080]to establish a testing environment that includes three living things.
[00:03:31.320]One, hungry insects that could feed on Arabidopsis, grow, and complete their life cycle.
[00:03:36.920]Two, Arabidopsis plants that were considered genetically normal.
[00:03:41.260]And three, Arabidopsis plants that were homozygous for the jar1 mutation.
[00:03:45.960]Scott Dvorak could grow the needed plants and then order the insects
[00:03:50.020]from a supplier once he had his plants ready for the experiment.
[00:03:53.400]The chosen insect was the cabbage looper.
[00:03:57.940]In the second part of this video, we will see how Scott set up his experiments
[00:04:02.500]to test his hypothesis that the plant uses jar1 to respond to insects.

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