WESTERN PRODUCER — Plants can tell time and their internal clocks can measure the rhythms of their environment.
Now, research conducted at the University of Cambridge in the United Kingdom has shown that this system could be exploited in a process scientists call “chronoculture” to enhance agriculture and improve global food security.
In the past 25 years, studies on plant circadian rhythms — a 24-hour oscillator adapted to living on a rotating planet — show that they profoundly affect plant physiology.
Thirty percent of genes are switched on and off by these circadian clocks, which also regulate metabolic events, flowering, biomass, photosynthesis, water use, temperature response and defence against pathogens, all of which impact crop yield.
“It has been known since the work of Charles Darwin and (his son) Francis Darwin that circadian clocks control a lot of movements of plants, but the importance was not understood,” said Alex Webb, chair of cell signalling in the university’s department of plant sciences.
“When I started my laboratory, we were growing plants with mutations that affect the timing of the circadian clock. We noticed that these plants often appeared a bit smaller than those plants with a normally functioning clock. We set out to test this hypothesis formally as a side project, and we were surprised that the effect can be very large (clock mutants can be 50 percent smaller than wild type). We then realized that we should be able to see similar affects in wild-type plants if the total environment period was different to 24 hours and again, we found that growth of the wild-type plants was affected.”
He said that while a plant’s internal clock works with a 24-hour period, for it to work properly, it also needs to set to local time.
“The clock is reset every day by dawn and dusk, and by temperature cycles, so that it tracks local time and allows the plant to anticipate the next sunrise. Away from the equator, the timing of sunrise and sunset can change dramatically across the seasons. Where I live in Cambridge U.K., sunrise varies by four hours across the year. So, the clocks respond to the daily rhythms of light/dark, warmth and cold to set the time. But they also need to tick accurately and be buffered against short-term changes in temperature, such as occur through weather. We call this temperature compensation.”
Webb said an important area that has not received enough research is that the circadian clock can affect the way in which a plant can respond to changes in the environment. Lab study plants like arabidopsis are more responsive to cold stress in the day than at night.
“I think this might be one of the most important functions of circadian clocks, providing time of day context for responses to environmental signals,” he said. “Cold during the night is to be expected, but cold during the day might indicate a change in seasons. The plant needs to mount a greater response to prepare for winter.”
One of the most important agricultural aspects of circadian biology is that the clock acts as the internal chronometer by which plants measure the length of day and the change of seasons. Day length regulates many biological functions such as the switch from producing leaf material to producing reproductive flowers. Webb said this is called photoperiodism.
“For this reason, we see that variation in circadian clock genes have been selected for by breeders, knowingly or unknowingly, to change the time when crops flower. This can be one of the most important yield determinants. We have recently reported that one of the circadian clock genes, Early Flowering 3, or ELF3, is a candidate gene that can be used to regulate the flowering time of wheat. We have shown that this gene, as well as being part of the circadian clock directly, regulates the flowering time process.”
The genes controlling the circadian rhythm are similar in all major crops, making them a good target for crop breeders wanting to gain more control over certain functions. This approach to chronoculture could be applied through three approaches.
One approach is to apply treatments such as water, chemicals and fertilizers at the time of day when they are most effective, thus reducing the inputs to the system. This could also be aligned with growing crops vertically indoors using LED lighting. This puts crop production in a local, pest-free environment.
“This is exciting because the total environment can be controlled, including the timing and colour of the lighting,” said Webb. “This is the first time that people have had the opportunity to totally control the genetics and environment of plant growth.”
Total control offers crop production for specialist needs in otherwise challenging locations such as deserts. He said they are also working with partners at the University of Adelaide in Australia to consider how best to grow crops in space and take advantage of the new research.
Another challenge for indoor agriculture is to grow larger species but with less energy consumption. Webb’s lab has been collaborating with Vertical Future, a rapidly growing young company in various U.K. locations, to identify lighting and mineral treatments optimizing lettuce growth indoors.
A second chronoculture approach is through robotics and automated monitoring to bypass the human circadian rhythm. This would be a system to measure plant health, provide treatments and harvest crops across the standard 24-hour cycle but without human intervention. He said some approaches may be expensive while others more economic depending on rapidly reducing costs because of sophisticated electronics.
The third approach is breeding. While breeders have already brought about improvements in crops by fine-tuning flowering times or adapting plants to grow at higher latitudes, they will be able to pursue these adaptations more thoroughly now that they know the genes to select for.
“The process can be done with more precision and greater speed using gene-editing approaches,” he said. “Gene editing is more appealing than GMO due to the more subtle and directed changes we can make.”
Genetic modification has received a lot of resistance in the U.K. and Europe. However, Wells said that the U.K. government is liberalizing the rules around gene editing to bring them more into line with the rest of the world.
“Europe has been traditionally resistant to genetic engineering approaches such as GMO and gene editing, possibly because of a perceived lack of benefit for the public. However, surveys indicate that public attitudes in Europe to gene editing are softening, perhaps because of the promise of rapidly tangible benefits for the consumer, such as blight resistant potatoes.”
The application of chronoculture offers a bright future for agriculture but research is still in the formative stages.
