Cambridge scientists at Sainsbury Laboratory make discovery that could secure future harvests
The fertile Fenland soil has delivered many a bumper harvest to Cambridgeshire down the years. Good harvests have always been vital to human society, and they matter now as much as they ever have – more, in a steadily warming world with a growing population to feed.
Now an international team, led by scientists from the University of Cambridge, has made a discovery that may help to secure future harvests by breeding tougher plants.
They’ve found that plants contain a molecule which by day is sensitive to light, but after dark switches to do something else entirely: by night it responds not to light, but to temperature. And temperature is playing an ever-larger part in the sort of harvests we can hope for. Exceptionally hot summers can devastate agricultural yields, and the frequency of hot summers is increasing, with 15 of the 16 hottest years recorded occurring since 2000.
The lead researcher is Dr Philip Wigge, from Cambridge’s Sainsbury Laboratory in Bateman Street.
He says: “It’s estimated that agricultural yields will need to double by 2050, but climate change is a major threat to such targets. Key crops such as wheat and rice are sensitive to high temperatures. Thermal stress reduces crop yields by around 10 per cent for every 1 deg C increase in temperature.”
He stresses that the team’s work involves “basic science research”, and that predicting how useful it may prove is difficult. But he offers several pointers. “There is some urgency to accelerate the breeding of crops resilient to heat stress,” he says. “We believe these findings can contribute to this. Similarly, our breakthrough will help other plant scientists to understand plants better. In the future, it’s quite possible that research such as this could be used in other ways, for example to breed garden plants to be more adapted to particular climates.”
Humans have known since we first began to farm that plants respond to temperature. But Wigge says his team has taken that knowledge a step further.
“What people have been looking for all this time is a molecule that directly senses temperature itself and transmits this information,” he explains. “While it has been clear that plants respond very quickly to temperature, how they do this has not been understood. We now know the molecules that detect temperature and transmit this to the rest of the plant to control how it grows and develops.”
The photoreceptor molecules in the plants’ cells, called phytochromes, act in the dark to control genetic switches in response to temperature, enabling the plants to develop according to seasonal temperature changes. They go from their active, light-detecting state to a state of inactivity at a pace “directly proportional to temperature”, say the researchers, like mercury in a thermometer. The warmer it is, the faster the molecules change state and stimulate plant growth.
Dr Wigge explains how the process works, allowing the molecules not just to measure temperature but to use that to stimulate the plants’ growth: “The phytochromes measure temperature directly by becoming inactivated. This amounts to removing the brakes on growth. When phytochrome activity goes down, growth goes up via the activity of growth-promoting proteins that are no longer inhibited. Growth slows down during the autumn and winter and picks up again in the warmer spring.”
In their active state phytochromes are triggered by sunlight and bind themselves to DNA to restrict growth. This can in fact benefit the plants.
He says: “Everything is a trade-off in nature. By growing more slowly, plants are likely to have more resources available for other activities such as withstanding pests and stresses.”
If a plant finds itself in shade, phytochromes are quickly inactivated – enabling it to grow faster to find sunlight again. This is how plants compete to escape each other’s shade. “Light-driven changes to phytochrome activity occur very fast, in less than a second,” says Dr Wigge.
The new findings are the culmination of 12 years of research involving scientists from Germany, Argentina and the US, led by the Cambridge team. The work was modelled in a mustard plant called Arabidopsis, but the phytochrome genes necessary for temperature sensing are found in crop plants as well.
The research explains a lot about growth response to both temperature and daylight length: if a plant had two control systems, then it could get confused on a cold summer day, or a hot winter one. To have one command centre for both factors is a reminder that evolution isn’t just clever: it’s very clever.
Dr Wigge doesn’t know of any similar dual-use molecules, but he doesn’t rule them out.
“There’s a family of transcription factors [proteins that bind to DNA and regulate gene expression] that responds to hormones, light and temperature. So, in a way, by integrating different environmental signals, these transcription factors are behaving analogously to the phytochromes.”
He’s cautiously hopeful that the discovery of the molecules’ double life could mean progress.
“Now we’ve identified the role of phytochromes, we can ask if different versions of them can be engineered that change the temperature responses of crop plants,” says Dr Wigge. “This would enable us to rewire the plants to have an altered response to warm temperature. This is a long-term project however, and there will likely be surprises along the way.”
The tradition of the horkey
Do you know what a horkey is – or was? In Eastern England, till relatively recently, it meant the harvest celebrations.
In Whittlesford, for instance, the last load of corn (the Horkey Load) was carried in on a decorated cart bearing the harvesters, the Lord of the Harvest and his Queen.
The reapers would shout: “Horkey home! Now water!” The climax was a feast: mountains of roast beef, plum pudding and local strong ale, all paid for by the farmer. Some Cambridgeshire villagers would perform a dance wearing stiff straw hats on which they balanced tankards of ale.
One reason for the disappearance of the custom seems to have been a growing parsimony on the part of those who had traditionally funded it, if a 20th-century writer is to be believed: “Since the passing of the Agricultural Wages Bill [of 1924], the Horkey has been generally abandoned, though one or two landowners in the eastern counties are still generous enough to give a supper each year.”
Dr Wigge and his colleagues have extended our knowledge of how plants behave, and why.
But our ancestors often had a shrewd idea of what was likely to happen anyway. The researchers say the phytochromes’ dual role explains a familiar rhyme long used to predict the coming season: “Oak before Ash, we’ll have a splash: Ash before Oak, we’re in for a soak.”
“Oak trees rely much more on temperature, likely using phytochromes as thermometers to dictate development, whereas ash trees rely on measuring day-length to determine their seasonal timing,” he says.
“A warmer spring, and consequently a higher likelihood of a hot summer, will result in oak leafing before ash. A cold spring will see the opposite. As the British know only too well, a colder summer is likely to be a rain-soaked one.”
Knowing more about plants’ responses to their environment can help not only scientists and growers but gardeners too. While some plants mainly use day-length as an indicator of the season, others, such as daffodils, are highly sensitive to temperature and can flower months in advance during a warm winter.