1 00:00:05.490 --> 00:00:09.990 These genes that are activated, these genes that are transcribed immediately 2 00:00:09.990 --> 00:00:16.450 after touching, the arabidopsis plant, barometer colleagues called touch genes. 3 00:00:17.780 --> 00:00:19.180 And the first of these touch genes 4 00:00:19.180 --> 00:00:22.360 that she studied encodes a protein called calmodulin. 5 00:00:22.360 --> 00:00:26.090 Now, I know this is getting a little bit specific, but just bear with 6 00:00:26.090 --> 00:00:27.830 me, and you'll see why this story 7 00:00:27.830 --> 00:00:30.560 is important for understanding plant responses to 8 00:00:30.560 --> 00:00:35.050 tactile signaling, and its connection to human responses to tactile signaling. 9 00:00:36.420 --> 00:00:41.760 Calmodulin is a protein which is involved in calcium signalling within the cell. 10 00:00:43.590 --> 00:00:47.200 As I mentioned in the beginning of this lecture, calcium is one of the 11 00:00:47.200 --> 00:00:50.570 important salt ions that regulates a cell's 12 00:00:50.570 --> 00:00:54.369 electrical charge, and communcation between the cells. 13 00:00:55.380 --> 00:01:00.570 Calcium is the ion that's released when the action potential reaches the end of a 14 00:01:00.570 --> 00:01:06.040 nerve, causing the release of the neurotransmitters, enabling 15 00:01:06.040 --> 00:01:10.830 the propagation of the, of the actual potential to the neighboring nerve cell. 16 00:01:12.880 --> 00:01:16.560 So the first, one of the first genes that's activated, once 17 00:01:16.560 --> 00:01:22.040 is a plant is touched, is a calcium binding protein called calmodulin. 18 00:01:23.560 --> 00:01:28.070 In plant cells, calcium helps maintain the cell turgor, the pressure 19 00:01:28.070 --> 00:01:32.510 within the cell, like in the pulvenus of the, of the mimosa. 20 00:01:32.510 --> 00:01:36.209 And it's also part of the cell wall. Actually has many, many, many rolls. 21 00:01:38.260 --> 00:01:40.220 although we don't know how all of these roles are 22 00:01:40.220 --> 00:01:44.125 integrated, it's under intense study in many laboratories around the world. 23 00:01:44.125 --> 00:01:45.769 We also know that 24 00:01:45.769 --> 00:01:47.060 [UNKNOWN] 25 00:01:47.060 --> 00:01:51.730 mechanical stimulation, like shaking of a branch, or when a root, 26 00:01:51.730 --> 00:01:57.010 it hits a rock, the concentraion of the calcium ions peaks. 27 00:01:57.010 --> 00:01:59.430 It spikes very quickly and then drops. 28 00:02:00.590 --> 00:02:03.200 So this spike in the calcium concentration 29 00:02:03.200 --> 00:02:06.430 affects the charge across the cell membrane. 30 00:02:07.700 --> 00:02:11.830 But not only does it affect the electricity of the cell, the charge, 31 00:02:11.830 --> 00:02:16.790 it also directly affects multiple cellular functions 32 00:02:16.790 --> 00:02:21.210 and it does this through binding of calmodulin. 33 00:02:21.210 --> 00:02:24.780 So calmodulin is a very small, but important protein. 34 00:02:24.780 --> 00:02:30.090 And when it binds calcium, it affects many many many cellular processes. 35 00:02:30.090 --> 00:02:32.340 For example, human beings, the binding of 36 00:02:32.340 --> 00:02:36.340 calcium to calmodulin is important for memory, 37 00:02:36.340 --> 00:02:40.090 information, muscle function, and nerve growth. 38 00:02:41.330 --> 00:02:43.850 So getting back to plants. 39 00:02:43.850 --> 00:02:46.920 The first touch gene identified by Bram was calmodulin. 40 00:02:48.450 --> 00:02:50.950 In other words when you touch a plant, be it a arabidopsis or 41 00:02:50.950 --> 00:02:56.830 papaya, one of the first thing the plant does is it makes calmodulin. 42 00:02:57.990 --> 00:03:01.590 Possibly, a plant makes more calmodulin to work 43 00:03:01.590 --> 00:03:05.220 with the increased calcium that comes with the action potentials. 44 00:03:07.450 --> 00:03:12.500 So thanks to the continuing work of Bram and other scientists, we now know that 45 00:03:12.500 --> 00:03:17.602 over two percent of the 25,000 arabidopsis 46 00:03:17.602 --> 00:03:21.478 genes are activated when the plant is touched. 47 00:03:21.478 --> 00:03:24.800 These include calmodulin and other calcium related 48 00:03:24.800 --> 00:03:27.580 genes, but also a plethora of other genes. 49 00:03:27.580 --> 00:03:32.460 Think about it. 2% of the genes are activated when you 50 00:03:32.460 --> 00:03:35.050 touch a plant, or when an animal brushes up 51 00:03:35.050 --> 00:03:37.930 against it, or when the wind shakes its leaves. 52 00:03:39.280 --> 00:03:44.350 This is a surprisingly large number of genes and it just indicates how far 53 00:03:44.350 --> 00:03:51.120 reaching a plant's response to tactile sensation has to be in order to survive. 54 00:03:51.120 --> 00:03:54.710 That the plant, rooted in the soil, has to 55 00:03:54.710 --> 00:03:57.420 respond in multiple ways in order to modulate its growth, 56 00:03:57.420 --> 00:04:01.430 in order to modulate its own physiology, in order to 57 00:04:05.840 --> 00:04:08.510 survive in a changing environment. So 58 00:04:10.570 --> 00:04:13.870 we've seen vastly different reactions to touch. 59 00:04:13.870 --> 00:04:18.200 We've seen fast reactions, such as in a Venus Fly Trap. 60 00:04:18.200 --> 00:04:21.170 There are slow reactions which we haven't time to show such as 61 00:04:21.170 --> 00:04:23.940 root navigation, there are very, very, 62 00:04:23.940 --> 00:04:26.310 very slow responses such as thigmomorphogenesis, 63 00:04:26.310 --> 00:04:30.210 but what they all have in common is some type of electrical 64 00:04:30.210 --> 00:04:35.290 signal and at the far end some type of change in gene transcription.