How do plants cope with cold mornings?

As the sun rises on a cold, bright morning, humans have the option to either stay warm under the duvet or embrace the day with gusto. However, for plants that rely on photosynthesis, such a morning poses a significant threat. 

To combat this, plants have evolved unique mechanisms to cope with the chill, allowing them to adapt and survive even in the coldest of environments. Recent research conducted by scientists at the John Innes Centre has shed light on these fascinating mechanisms, uncovering a cold “coping” strategy controlled by the plant’s biological clock. This discovery holds promise for the future of agriculture, particularly in the development of climate-resilient crops.

“We’ve identified a new process that helps plants tolerate cold. It’s controlled by the biological clock of plants, and we think it could be especially important on cold, bright mornings,” explained Professor Antony Dodd.

By understanding how plants adapt to cold temperatures, researchers believe they could breed more robust crops, such as winter wheat and winter oilseed rape, that can better withstand chilly climates. 

“We think that the mechanism that we have discovered could provide greater resilience of photosynthesis to cold temperatures,” said Professor Dodd. “It represents an interesting target for future precision breeding of climate resilient crops.”

Cold temperatures can wreak havoc on plant cells, causing damage, particularly when combined with an excess of light or freezing temperatures. This is why bright, cold mornings pose a significant threat to plant life. 

To better understand how plants defend themselves against such conditions, the researchers sought to unravel the communication pathway between low temperatures and chloroplasts, the site of photosynthesis within a plant cell. Chloroplasts, which are essential for the growth of major crops, contain their own small genome, a relic of their evolutionary past as photosynthetic bacteria. Over time, many chloroplast genes migrated to the plant nuclear genome, but some essential genes remained within the chloroplasts.

In this study, the research team focused on one such gene, a bacterial genetic legacy called a sigma factor (SIG5). In bacteria, comparable sigma factors are known to contribute to temperature responses. By conducting experiments in controlled laboratory conditions, the researchers manipulated light exposure and subjected plants to periods of chilling to better understand the role of SIG5 in plant cold tolerance.

Studying the intricate rhythms of the plant biological or circadian clock can be challenging. However, by removing plants from their natural day-night cycle, researchers have gained valuable insights into the free-running rhythms of these clocks. Similar to humans, plant circadian clocks are aligned to the 24-hour cycle, serving as an internal timekeeper within cells and regulating a wide range of essential biological processes.

Recent experiments conducted by a collaborative team from the John Innes Centre, the University of Bristol, Tokyo Institute of Technology, Nippon Telegraph and Telephone Corporation in Japan, and Durham University, have revealed the sensitivity of the SIG5 gene to cold temperatures early in the morning, regulated by the circadian clock. 

The researchers believe that SIG5 operates as part of a signaling network connecting the plant nucleus to the chloroplasts, which in turn regulates activities that protect the plant against harmful environmental effects.

“If the temperature is cold, then some enzymes involved in photosynthesis break down quickly,” explained Professor Dodd. “So, we think the process that is controlled by the nucleus signals into the chloroplast to make more of these proteins. When the plant sees cold and light at the same time, they need to switch on this signaling process from nucleus to chloroplasts to make more of these photosynthesis proteins.”

The role of the biological clock in this process is to act like a gate that either allows or blocks the signal, a phenomenon known as circadian gating. 

“Plants could have evolved to be particularly responsive to it being light and cold, like a spring morning, because these are the conditions that damage the photosynthetic system,” said Professor Dodd. “At some point during evolution, they have selected for this sensitivity and co-opted this ancient mechanism. Like many such processes in plants, this one turns out to be under the control of the circadian clock.”

Having demonstrated the effectiveness of this mechanism in laboratory settings, the researchers’ next step is to examine its impact in the field. One potential application of this discovery is to modify the mechanism to further enhance cold tolerance, which could enable the cultivation of cold-sensitive plants, such as maize, in more northern latitudes.

This groundbreaking research not only enhances our understanding of plant biology but also has significant implications for the future of agriculture. As climate change continues to disrupt weather patterns and challenge the growth of crops, the ability to develop climate-resilient crops will be essential for ensuring food security. 

The discovery of the cold “coping” mechanism controlled by the plant’s biological clock opens up new possibilities for breeding hardier crops that can thrive even in cold climates, helping to safeguard the world’s food supply in the face of increasing environmental stressors.

The research is published in the journal Nature Plants.

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