In the year 2000, the complete Arabidopsis genome was sequenced. And as I mentioned earlier in today's lecture, Arabidopsis has more or less 25,000 genes. But scientists were surprised to find that among these 25,000, are quite a number of genes that are known as human disease genes. For example, Arabidopsis contains the gene for breast cancer, Brca1 and Brca2. Arabidopsis contains the gene for cystic fibrosis, which is called CFTR. And Arabidopsis contains the gene for hereditary deafness. Why would plants contain genes for breast cancer, or for cystic fibrosis? When they obviously don't have breasts, and they obviously don't have lungs? Well the name of the gene can be a little bit misleading. We called it the gene for cystic fibrosis, or the gene for breast cancer, because mutations in these genes, when the genes are no longer functional, the disease happens. Brca, the breast cancer gene, has a function in fixing DNA, in DNA repair. When the DNA is not repaired properly, cancer forms. The cystic fibrosis gene has a essential role in the transport of salts, of ions in the, in the, in the body. When this doesn't function properly. We have respiratory problems, as in cystic fibrosis. So what about hereditary deafness? Well, mutations in many, many genes can cause different types of deafness. But one of them, one of the genes that's afflicted in hereditary deafness is a gene that's called myosin. Myosin is a gene which effects cell structure. And let's see what happens in the inner ear of mice that have a mutation in this gene. What we see here is a picture of the hairs in the inner ear. These are the hairs that vibrate when sound signals hit the ear. These hairs vibrate back and forth, and that lets the mouse know what type of sound it's hearing. The exact same process happens in the human ear. A mutation in one specific myosin gene, causes these hairs not to form. Here we see a picture of a deaf mouse. It's actually a mouse that cannot hear. And we can see that one of the reasons it can't hear, or the reason it can't hear is that it's hairs do not form properly. So that when the sound waves come, there's no hairs that vibrate. Arabidopsis contain this exact gene. So what happens when Arabidopsis is mutated for this myosin. Now obviously, Arabidopsis doesn't have ears, it doesn't have an inner ear for there to be hairs formed. But Arabidopsis roots and indeed, all roots do contain hairs, which we call these root hairs. And here, you could see in this picture what root hairs look like on Arabidopsis root. Now here's the very cool part. When there's a mutation in this myosin gene in Arabidopsis, these root hairs don't form. Does this mean that these plants are deaf? No of course not, because plants don't hear, and they definitely don't hear through their roots. The root hairs are necessary for the plant to absorb water and nutrients from the soil. So the myosin gene is necessary for a hairlike structure to be formed. In animals, this hairlike structure enables us to hear. In plants, this hairlike structure enables the plant to drink, to absorb water from its roots. The fact that Arabidopsis contains the genes for hereditary deafness, and for breast cancer, and for cystic fibrosis implies that all the organisms that preceded Arabidopsis and humans in evolution also had to have these genes. These are genes that are necessary for cellular function. So, if we look at evolution, these genes must have been present in the unicellular organisms which were the precursors of both plant life and animal life. These genes were necessary for all cells to survive. So, animals have these genes. Plants have these genes. At the cellular level, their function is the same. At the functional level of the organism, you're going to get different types of results. Ears, hairs, versus root hairs, for example. So are plants deaf? So far all the research seems to see seems to lead to that conclusion. But, I just want to leave us with the idea that maybe we're not actually doing the correct experiments. I mean, music is obviously the wrong experiment. If we think evolutionary what relevance is music for plant evolution? Plants have been evolving for over a million years. Music has been around for how long? Rock and roll has been around for 50 years? So obviously music was not an evolutionary pressure on plant development. But could there be ecologically relevant sounds that do affect how plants develop, how plants adapt to their environment? So maybe we need to be looking for what these sounds are. And I just want to talk about one experiment that was actually published in a very reputable journal, that shows that roots can bend towards subsonic vibrations. So this, in this picture, what we see are roots are bending in the direction from where the subsonic vibrations are coming from, from sounds that we're deaf to ourselves. So while this is intriguing, I just have to set, give a caveat here that these experiments and these results need to be validated. They need to re, be repeated in other labs and so that we can, until then we can't really conclude that plants respond to sound. I want to leave you with one last example of how the popular press can misrepresent signs. The New York Times reported on July 1st, 2014, that Noisy Predators Put Plants on Alert, Study Finds. This article starts with the following sentence. It has long been known that some plants can respond to sound. But why would a plant evolve the ability to hear? Now researchers are reporting that one reason may be to defend itself against predators. Well, I hope you can understand that this opening has two problems. One, as we've learned here, it has long not been known that some plants can respond to sound. Second, they completely misreported a very interesting study. So what this study? Well two scientists from the University of Missouri, Heidi Apple and Reginald Colecroft wanted to test whether the plants could respond to the noise of an insect's chewing jaws by producing protective insect repelling chemicals. Clearly such a noise and a response if they could find one, would be ecologically relevant. So let's look at their experimental design. First, they recorded the vibrations produced by the jaws of a caterpillar. As it was eating a leaf. To record these vibrations, they put caterpillars upon the leaf of a plant and using very sensitive equipment, they recorded the vibrations experienced by the fed upon leaf. Then to experimentally reproduce this, to reproduce the caterpillar feeding vibrations. They put what they called a piezoelectric actuators under the leaf and attach it to the leaf using mounting wax. When they played the vibrations back to the untreated leaves, the leaves produced a family, a family of chemicals called glucosinolates. These are chemicals that give mustard their sharp taste, and they also happen to be poisonous for caterpillars. So if you don't understand what this piezoelectric actuator actually is, you would think that plants listen to the sound of the caterpillars foraging. But in actuality, this device is a min, is a mini vibrator. Here is a picture of the setup from the article itself. As you can see, it's not the plant that's experiencing the sound, it's literally responding to a mini vibrator that's been glued to the underside of the leaf. Physically shaking the leaf, with the same vibrations that the insect does. So it's not that the plant is listening, it's feeling. I must add though that the scientists themselves never talked about the plants hearing, but only talked about it responding to vibrations. So yet again, and for the time being, we're let without conclusive evidence that plants hear. But, I should say, I am open to any experiment that will change this paradigm. Perhaps, into the future I'll have to change this class to report such studies. So to sum up today's lecture, which has been talking about tactile sensitivity in both humans and plants. Touch, leads to an electric signal. In humans, we've seen various modalities. There's mechano reception, there's temperature reception, there's pain, and there's hearing. In plants, there seem to be only a few modalities. There's definitely mechano reception, there's no pain, there seems to be no hearing. But there is responses to temperature which I haven't gone into. Plants can differentiate between cold and heat. So that sums up todays lecture we'll meet again next week.
