How we can make crops survive without water | Jill Farrant

220,217 views ・ 2016-02-09

TED


Please double-click on the English subtitles below to play the video.

00:12
I believe that the secret to producing extremely drought-tolerant crops,
0
12840
4216
00:17
which should go some way to providing food security in the world,
1
17080
3216
00:20
lies in resurrection plants,
2
20320
2696
00:23
pictured here, in an extremely droughted state.
3
23040
3136
00:26
You might think that these plants look dead,
4
26200
2856
00:29
but they're not.
5
29080
1296
00:30
Give them water,
6
30400
1456
00:31
and they will resurrect, green up, start growing, in 12 to 48 hours.
7
31880
5440
00:38
Now, why would I suggest
8
38320
1296
00:39
that producing drought-tolerant crops will go towards providing food security?
9
39640
4440
00:45
Well, the current world population is around 7 billion.
10
45040
3896
00:48
And it's estimated that by 2050,
11
48960
2496
00:51
we'll be between 9 and 10 billion people,
12
51480
2696
00:54
with the bulk of this growth happening in Africa.
13
54200
2880
00:57
The food and agricultural organizations of the world
14
57880
2456
01:00
have suggested that we need a 70 percent increase
15
60360
3136
01:03
in current agricultural practice
16
63520
2176
01:05
to meet that demand.
17
65720
1240
01:07
Given that plants are at the base of the food chain,
18
67720
2696
01:10
most of that's going to have to come from plants.
19
70440
2320
01:13
That percentage of 70 percent
20
73360
2696
01:16
does not take into consideration the potential effects of climate change.
21
76080
4216
01:20
This is taken from a study by Dai published in 2011,
22
80320
4240
01:25
where he took into consideration
23
85240
1936
01:27
all the potential effects of climate change
24
87200
2376
01:29
and expressed them -- amongst other things --
25
89600
2136
01:31
increased aridity due to lack of rain or infrequent rain.
26
91760
4616
01:36
The areas in red shown here,
27
96400
1776
01:38
are areas that until recently
28
98200
2056
01:40
have been very successfully used for agriculture,
29
100280
3176
01:43
but cannot anymore because of lack of rainfall.
30
103480
2400
01:46
This is the situation that's predicted to happen in 2050.
31
106640
2920
01:50
Much of Africa, in fact, much of the world,
32
110840
2176
01:53
is going to be in trouble.
33
113040
1896
01:54
We're going to have to think of some very smart ways of producing food.
34
114960
3656
01:58
And preferably among them, some drought-tolerant crops.
35
118640
3296
02:01
The other thing to remember about Africa is
36
121960
2056
02:04
that most of their agriculture is rainfed.
37
124040
2800
02:08
Now, making drought-tolerant crops is not the easiest thing in the world.
38
128080
3456
02:11
And the reason for this is water.
39
131560
2416
02:14
Water is essential to life on this planet.
40
134000
3136
02:17
All living, actively metabolizing organisms,
41
137160
4135
02:21
from microbes to you and I,
42
141320
2056
02:23
are comprised predominately of water.
43
143400
2336
02:25
All life reactions happen in water.
44
145760
2536
02:28
And loss of a small amount of water results in death.
45
148320
3016
02:31
You and I are 65 percent water --
46
151360
2056
02:33
we lose one percent of that, we die.
47
153440
1720
02:35
But we can make behavioral changes to avoid that.
48
155840
2720
02:39
Plants can't.
49
159920
1576
02:41
They're stuck in the ground.
50
161520
1616
02:43
And so in the first instance they have a little bit more water than us,
51
163160
3376
02:46
about 95 percent water,
52
166560
1256
02:47
and they can lose a little bit more than us,
53
167840
2096
02:49
like 10 to about 70 percent, depending on the species,
54
169960
2960
02:54
but for short periods only.
55
174000
1360
02:56
Most of them will either try to resist or avoid water loss.
56
176680
4176
03:00
So extreme examples of resistors can be found in succulents.
57
180880
3936
03:04
They tend to be small, very attractive,
58
184840
2816
03:07
but they hold onto their water at such great cost
59
187680
2736
03:10
that they grow extremely slowly.
60
190440
2000
03:13
Examples of avoidance of water loss are found in trees and shrubs.
61
193440
4576
03:18
They send down very deep roots,
62
198040
1576
03:19
mine subterranean water supplies
63
199640
1696
03:21
and just keep flushing it through them at all times,
64
201360
2456
03:23
keeping themselves hydrated.
65
203840
1856
03:25
The one on the right is called a baobab.
66
205720
1976
03:27
It's also called the upside-down tree,
67
207720
2056
03:29
simply because the proportion of roots to shoots is so great
68
209800
3776
03:33
that it looks like the tree has been planted upside down.
69
213600
2696
03:36
And of course the roots are required for hydration of that plant.
70
216320
3240
03:40
And probably the most common strategy of avoidance is found in annuals.
71
220760
4520
03:45
Annuals make up the bulk of our plant food supplies.
72
225840
3176
03:49
Up the west coast of my country,
73
229040
1696
03:50
for much of the year you don't see much vegetation growth.
74
230760
3536
03:54
But come the spring rains, you get this:
75
234320
2656
03:57
flowering of the desert.
76
237000
1240
03:59
The strategy in annuals,
77
239000
1856
04:00
is to grow only in the rainy season.
78
240880
2360
04:03
At the end of that season they produce a seed,
79
243960
2296
04:06
which is dry, eight to 10 percent water,
80
246280
2816
04:09
but very much alive.
81
249120
1656
04:10
And anything that is that dry and still alive,
82
250800
2896
04:13
we call desiccation-tolerant.
83
253720
1480
04:15
In the desiccated state,
84
255840
1416
04:17
what seeds can do is lie in extremes of environment
85
257280
2656
04:19
for prolonged periods of time.
86
259960
1656
04:21
The next time the rainy season comes,
87
261640
2216
04:23
they germinate and grow,
88
263880
1496
04:25
and the whole cycle just starts again.
89
265400
1880
04:28
It's widely believed that the evolution of desiccation-tolerant seeds
90
268120
4056
04:32
allowed the colonization and the radiation
91
272200
2176
04:34
of flowering plants, or angiosperms, onto land.
92
274400
3520
04:38
But back to annuals as our major form of food supplies.
93
278960
3160
04:42
Wheat, rice and maize form 95 percent of our plant food supplies.
94
282800
4720
04:48
And it's been a great strategy
95
288480
1536
04:50
because in a short space of time you can produce a lot of seed.
96
290040
3176
04:53
Seeds are energy-rich so there's a lot of food calories,
97
293240
2620
04:55
you can store it in times of plenty for times of famine,
98
295884
3920
05:00
but there's a downside.
99
300480
1240
05:02
The vegetative tissues,
100
302560
1376
05:03
the roots and leaves of annuals,
101
303960
2176
05:06
do not have much
102
306160
1256
05:07
by way of inherent resistance, avoidance or tolerance characteristics.
103
307440
4096
05:11
They just don't need them.
104
311560
1296
05:12
They grow in the rainy season
105
312880
1416
05:14
and they've got a seed to help them survive the rest of the year.
106
314320
3376
05:17
And so despite concerted efforts in agriculture
107
317720
2696
05:20
to make crops with improved properties
108
320440
2536
05:23
of resistance, avoidance and tolerance --
109
323000
2176
05:25
particularly resistance and avoidance
110
325200
1896
05:27
because we've had good models to understand how those work --
111
327120
2896
05:30
we still get images like this.
112
330040
2336
05:32
Maize crop in Africa,
113
332400
1456
05:33
two weeks without rain
114
333880
1416
05:35
and it's dead.
115
335320
1200
05:37
There is a solution:
116
337560
1240
05:39
resurrection plants.
117
339520
1240
05:41
These plants can lose 95 percent of their cellular water,
118
341320
3776
05:45
remain in a dry, dead-like state for months to years,
119
345120
3856
05:49
and give them water,
120
349000
1736
05:50
they green up and start growing again.
121
350760
1880
05:53
Like seeds, these are desiccation-tolerant.
122
353560
3296
05:56
Like seeds, these can withstand extremes of environmental conditions.
123
356880
4120
06:01
And this is a really rare phenomenon.
124
361760
2016
06:03
There are only 135 flowering plant species that can do this.
125
363800
4376
06:08
I'm going to show you a video
126
368200
1416
06:09
of the resurrection process of these three species
127
369640
2616
06:12
in that order.
128
372280
1216
06:13
And at the bottom,
129
373520
1256
06:14
there's a time axis so you can see how quickly it happens.
130
374800
2736
06:56
(Applause)
131
416160
2040
07:02
Pretty amazing, huh?
132
422240
1536
07:03
So I've spent the last 21 years trying to understand how they do this.
133
423800
4216
07:08
How do these plants dry without dying?
134
428040
2400
07:11
And I work on a variety of different resurrection plants,
135
431080
2776
07:13
shown here in the hydrated and dry states,
136
433880
2416
07:16
for a number of reasons.
137
436320
1456
07:17
One of them is that each of these plants serves as a model
138
437800
2856
07:20
for a crop that I'd like to make drought-tolerant.
139
440680
2376
07:23
So on the extreme top left, for example, is a grass,
140
443080
2936
07:26
it's called Eragrostis nindensis,
141
446040
2256
07:28
it's got a close relative called Eragrostis tef --
142
448320
2376
07:30
a lot of you might know it as "teff" --
143
450720
2016
07:32
it's a staple food in Ethiopia,
144
452760
1736
07:34
it's gluten-free,
145
454520
1256
07:35
and it's something we would like to make drought-tolerant.
146
455800
3016
07:38
The other reason for looking at a number of plants,
147
458840
2416
07:41
is that, at least initially,
148
461280
1376
07:42
I wanted to find out: do they do the same thing?
149
462680
2256
07:44
Do they all use the same mechanisms
150
464960
1696
07:46
to be able to lose all that water and not die?
151
466680
2576
07:49
So I undertook what we call a systems biology approach
152
469280
2696
07:52
in order to get a comprehensive understanding
153
472000
2176
07:54
of desiccation tolerance,
154
474200
2016
07:56
in which we look at everything
155
476240
1456
07:57
from the molecular to the whole plant, ecophysiological level.
156
477720
2912
08:00
For example we look at things like
157
480657
1634
08:02
changes in the plant anatomy as they dried out
158
482316
2197
08:04
and their ultrastructure.
159
484537
1239
08:05
We look at the transcriptome, which is just a term for a technology
160
485800
3176
08:09
in which we look at the genes
161
489000
1416
08:10
that are switched on or off, in response to drying.
162
490440
2416
08:12
Most genes will code for proteins, so we look at the proteome.
163
492880
3216
08:16
What are the proteins made in response to drying?
164
496120
2400
08:19
Some proteins would code for enzymes which make metabolites,
165
499480
3896
08:23
so we look at the metabolome.
166
503400
1576
08:25
Now, this is important because plants are stuck in the ground.
167
505000
3296
08:28
They use what I call a highly tuned chemical arsenal
168
508320
4096
08:32
to protect themselves from all the stresses of their environment.
169
512440
3416
08:35
So it's important that we look
170
515880
1496
08:37
at the chemical changes involved in drying.
171
517400
2440
08:40
And at the last study that we do at the molecular level,
172
520520
2656
08:43
we look at the lipidome --
173
523200
1256
08:44
the lipid changes in response to drying.
174
524480
2055
08:46
And that's also important
175
526559
1257
08:47
because all biological membranes are made of lipids.
176
527840
2815
08:50
They're held as membranes because they're in water.
177
530679
2577
08:53
Take away the water, those membranes fall apart.
178
533280
2240
08:56
Lipids also act as signals to turn on genes.
179
536240
3040
09:00
Then we use physiological and biochemical studies
180
540200
2696
09:02
to try and understand the function of the putative protectants
181
542920
3216
09:06
that we've actually discovered in our other studies.
182
546160
2936
09:09
And then use all of that to try and understand
183
549120
2176
09:11
how the plant copes with its natural environment.
184
551320
2320
09:15
I've always had the philosophy that I needed a comprehensive understanding
185
555480
4336
09:19
of the mechanisms of desiccation tolerance
186
559840
2256
09:22
in order to make a meaningful suggestion for a biotic application.
187
562120
3840
09:27
I'm sure some of you are thinking,
188
567000
1656
09:28
"By biotic application,
189
568680
1256
09:29
does she mean she's going to make genetically modified crops?"
190
569960
2920
09:34
And the answer to that question is:
191
574240
1696
09:35
depends on your definition of genetic modification.
192
575960
2381
09:39
All of the crops that we eat today, wheat, rice and maize,
193
579200
2816
09:42
are highly genetically modified from their ancestors,
194
582040
3216
09:45
but we don't consider them GM
195
585280
1976
09:47
because they're being produced by conventional breeding.
196
587280
2640
09:50
If you mean, am I going to put resurrection plant genes into crops,
197
590880
3776
09:54
your answer is yes.
198
594680
1296
09:56
In the essence of time, we have tried that approach.
199
596000
3136
09:59
More appropriately, some of my collaborators at UCT,
200
599160
2856
10:02
Jennifer Thomson, Suhail Rafudeen,
201
602040
1936
10:04
have spearheaded that approach
202
604000
1616
10:05
and I'm going to show you some data soon.
203
605640
1953
10:09
But we're about to embark upon an extremely ambitious approach,
204
609200
4016
10:13
in which we aim to turn on whole suites of genes
205
613240
3456
10:16
that are already present in every crop.
206
616720
2696
10:19
They're just never turned on under extreme drought conditions.
207
619440
2905
10:22
I leave it up to you to decide
208
622800
1456
10:24
whether those should be called GM or not.
209
624280
1953
10:27
I'm going to now just give you some of the data from that first approach.
210
627560
3456
10:31
And in order to do that
211
631040
1256
10:32
I have to explain a little bit about how genes work.
212
632320
2656
10:35
So you probably all know
213
635000
1256
10:36
that genes are made of double-stranded DNA.
214
636280
2056
10:38
It's wound very tightly into chromosomes
215
638360
1936
10:40
that are present in every cell of your body or in a plant's body.
216
640320
3160
10:44
If you unwind that DNA, you get genes.
217
644080
3080
10:47
And each gene has a promoter,
218
647840
2456
10:50
which is just an on-off switch,
219
650320
2376
10:52
the gene coding region,
220
652720
1416
10:54
and then a terminator,
221
654160
1256
10:55
which indicates that this is the end of this gene, the next gene will start.
222
655440
3600
10:59
Now, promoters are not simple on-off switches.
223
659720
2896
11:02
They normally require a lot of fine-tuning,
224
662640
2696
11:05
lots of things to be present and correct before that gene is switched on.
225
665360
4040
11:10
So what's typically done in biotech studies
226
670240
3056
11:13
is that we use an inducible promoter,
227
673320
1816
11:15
we know how to switch it on.
228
675160
1576
11:16
We couple that to genes of interest
229
676760
2016
11:18
and put that into a plant and see how the plant responds.
230
678800
2680
11:22
In the study that I'm going to talk to you about,
231
682120
2576
11:24
my collaborators used a drought-induced promoter,
232
684720
2456
11:27
which we discovered in a resurrection plant.
233
687200
2416
11:29
The nice thing about this promoter is that we do nothing.
234
689640
3136
11:32
The plant itself senses drought.
235
692800
2080
11:35
And we've used it to drive antioxidant genes from resurrection plants.
236
695600
5096
11:40
Why antioxidant genes?
237
700720
1856
11:42
Well, all stresses, particularly drought stress,
238
702600
3056
11:45
results in the formation of free radicals,
239
705680
2296
11:48
or reactive oxygen species,
240
708000
2336
11:50
which are highly damaging and can cause crop death.
241
710360
2720
11:53
What antioxidants do is stop that damage.
242
713680
2600
11:57
So here's some data from a maize strain that's very popularly used in Africa.
243
717360
3896
12:01
To the left of the arrow are plants without the genes,
244
721280
3296
12:04
to the right --
245
724600
1256
12:05
plants with the antioxidant genes.
246
725880
2056
12:07
After three weeks without watering,
247
727960
1816
12:09
the ones with the genes do a hell of a lot better.
248
729800
2480
12:13
Now to the final approach.
249
733720
1336
12:15
My research has shown that there's considerable similarity
250
735080
3536
12:18
in the mechanisms of desiccation tolerance in seeds and resurrection plants.
251
738640
4416
12:23
So I ask the question,
252
743080
1416
12:24
are they using the same genes?
253
744520
1440
12:26
Or slightly differently phrased,
254
746480
2256
12:28
are resurrection plants using genes evolved in seed desiccation tolerance
255
748760
4496
12:33
in their roots and leaves?
256
753280
1256
12:34
Have they retasked these seed genes
257
754560
2056
12:36
in roots and leaves of resurrection plants?
258
756640
2040
12:39
And I answer that question,
259
759760
1856
12:41
as a consequence of a lot of research from my group
260
761640
2416
12:44
and recent collaborations from a group of Henk Hilhorst in the Netherlands,
261
764080
3536
12:47
Mel Oliver in the United States
262
767640
1576
12:49
and Julia Buitink in France.
263
769240
2600
12:51
The answer is yes,
264
771880
1416
12:53
that there is a core set of genes that are involved in both.
265
773320
2856
12:56
And I'm going to illustrate this very crudely for maize,
266
776200
3416
12:59
where the chromosomes below the off switch
267
779640
2416
13:02
represent all the genes that are required for desiccation tolerance.
268
782080
3575
13:05
So as maize seeds dried out at the end of their period of development,
269
785680
4256
13:09
they switch these genes on.
270
789960
1360
13:12
Resurrection plants switch on the same genes
271
792680
2896
13:15
when they dry out.
272
795600
1656
13:17
All modern crops, therefore,
273
797280
1776
13:19
have these genes in their roots and leaves,
274
799080
2056
13:21
they just never switch them on.
275
801160
1736
13:22
They only switch them on in seed tissues.
276
802920
1960
13:25
So what we're trying to do right now
277
805440
1736
13:27
is to understand the environmental and cellular signals
278
807200
2616
13:29
that switch on these genes in resurrection plants,
279
809840
2440
13:33
to mimic the process in crops.
280
813280
1760
13:35
And just a final thought.
281
815680
1736
13:37
What we're trying to do very rapidly
282
817440
2216
13:39
is to repeat what nature did in the evolution of resurrection plants
283
819680
3816
13:43
some 10 to 40 million years ago.
284
823520
1840
13:46
My plants and I thank you for your attention.
285
826160
2496
13:48
(Applause)
286
828680
6235
About this website

This site will introduce you to YouTube videos that are useful for learning English. You will see English lessons taught by top-notch teachers from around the world. Double-click on the English subtitles displayed on each video page to play the video from there. The subtitles scroll in sync with the video playback. If you have any comments or requests, please contact us using this contact form.

https://forms.gle/WvT1wiN1qDtmnspy7