How plants cope with the cold light of day - and why it matters for future crops
IMAGE: RESEARCH LED BY THE JOHN INNES CENTRE HAS DISCOVERED A COLD “COPING” MECHANISM THAT IS UNDER THE CONTROL OF THE PLANT BIOLOGICAL CLOCK view more
CREDIT: DR DORA CANO-RAMIREZ.
On bright chilly mornings you can either snuggle down under the duvet or leap up and seize the day.
However, for photosynthesising plants, this kind of dawn spells danger, so they have evolved their own way of making cold mornings tolerable.
Research led by the John Innes Centre has discovered a cold “coping” mechanism that is under the control of the plant biological clock and could offer solutions to breeding more resilience into crops less suited to cold climates.
“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,” says Professor Antony Dodd, a group leader at the John Innes Centre.
“Crops such as winter wheat and winter oilseed rape experience cold temperatures for periods of their cultivation,” he continues. “We think that the mechanism that we have discovered could provide greater resilience of photosynthesis to cold temperatures. It represents an interesting target for future precision breeding of climate resilient crops.”
Cold temperatures can damage plant cells, particularly when combined with too much light or during freezing temperatures. Hence why those bright cold mornings are so dangerous to plants.
The researchers wanted to know how information about low temperatures is communicated to the chloroplasts, the site of photosynthesis inside a plant cell, essential for all our major crops.
Chloroplasts contain their own small genome that reflects their evolutionary past as photosynthetic bacteria, before they were engulfed and co-opted by plants to carry out photosynthesis. Throughout evolution many genes from the chloroplast transferred to the plant nuclear genome, but chloroplasts have held on to some essential genes.
In this research the team focussed on one such bacterial genetic legacy called a sigma factor (SIG5). In bacteria, comparable sigma factors contribute to responses to temperature.
In experiments conducted under controlled laboratory conditions they manipulated the light conditions, and subjected plants to periods of chilling.
Removing plants from the day night cycle enables researchers to better study the free-running rhythms of the plant biological or circadian clock. In plants, as in humans, the clock is aligned to the 24-hour cycle, offering a measure of time inside cells, and regulating a range of essential biological processes.
The experiments showed sensitivity of the SIG5 gene to cold treatment early in the morning, under the control of the circadian clock.
The team theorise that SIG5 operates as part of a signalling network that links the plant nucleus to the chloroplasts, regulating activities that can protect the plant against harmful environmental effects.
“If the temperature is cold then some enzymes involved in photosynthesis break down quickly.” explains 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 signalling process from nucleus to chloroplasts to make more of these photosynthesis proteins.”
The role of the biological clock is to act like a gate that either lets the signal through or not, a process 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. 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.”
The mechanism has been shown to work in the lab. The next stage of this research is to understand the impact of this process in the field. One intriguing application is to see if the mechanism can be modified to further increase cold tolerance, for example to grow plants that are less tolerant of cold, such as maize, at more northern latitudes.
The research is a collaboration between the John Innes Centre, the University of Bristol, Tokyo Institute of Technology and Nippon Telegraph and Telephone Corporation in Japan, and Durham University.
Low-temperature and circadian signals are integrated by the sigma factor SIG5, appears in Nature Plants.
JOURNAL
Nature Plants
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Cells
ARTICLE TITLE
Low-temperature and circadian signals are integrated by the sigma factor SIG5
ARTICLE PUBLICATION DATE
30-Mar-2023
How plants adapt to nitrogen deficiency
Researchers at the University of Bonn discover gene variants in wheat and barley that improve nitrogen utilization
Peer-Reviewed PublicationIMAGE: WHEAT VARIETIES WITH A SPECIFIC NPF2.12 GENE VARIANT (RIGHT) HAVE SIGNIFICANTLY BETTER ROOT GROWTH AT LOW NITROGEN LEVELS IN THE SOIL THAN VARIETIES WITHOUT THIS GENE VARIANT (LEFT). view more
CREDIT: © MD. NUREALAM SIDDIQUI
"We studied a large number of wheat and barley genotypes under different nitrogen supply conditions and analyzed their root architecture and nitrogen accumulation in the plants," says lead author Md. Nurealam Sidiqqui of the Plant Breeding group at the University of Bonn's Institute of Crop Science and Resource Conservation (INRES). The researchers studied a total of more than 220 different wheat and barley varieties from the last half century of plant breeding. "The wheat varieties studied were selected to cover the breeding history over the last 60 years," explains Prof. Dr. Jens Léon of INRES Plant Breeding.
At the University of Bonn's agricultural research campus Klein-Altendorf, the researchers studied these different varieties on trial plots with high nitrogen levels and, for comparison, on plots with low nitrogen application. The team then analyzed, among other aspects root traits characteristics and the nitrogen content of leaves and grains of each variety, and performed genome-wide genetic analyses to find correlations between DNA sequences and the corresponding traits, Prof. Léon further explains.
More roots take up more nitrogen from the soil
During the evaluation, the researchers came across NPF2.12. Certain variants of this gene caused plants to develop larger root systems when soil nitrogen supply was poor. "It is likely that the gene, or rather the protein it encodes, acts as a sensor that needs to be switched off when nitrogen levels in the soil are low in order to indirectly increase the messenger nitric oxide as part of a signaling cascade, which in turn induces root growth, thereby improving nitrogen utilization," says Dr. Agim Ballvora from the INRES Plant Breeding, who is the paper’s corresponding author.
"Under low nitrogen conditions and in the presence of certain variants of the NPF2.12 gene, increased nitrogen content in leaves and grains is detectable compared to high nitrogen availability," says Ballvora, who also collaborates with the PhenoRob Cluster of Excellence at the University of Bonn. Consequently, under adverse conditions these varieties give higher yield than those containing the alternative allele, emphasizes Siddiqui.
Variants of the NPF2.12 nitrate sensor help with nitrogen utilization
The researchers could demonstrate both in the laboratory and in the greenhouse that NPF2.12 is indeed responsible for this improved performance. Wheat plants with a defect in the NPF2.12 gene were analyzed. When nitrogen supply was poor, the corresponding lines having the defect npf2.12 allele behaved like cultivars that inherently have the helpful gene variant. "These results show that NPF2.12 is a negative regulator, whose reduced expression in corresponding cultivars results in more root growth and higher nitrogen content in the shoot through a sophisticated mechanism," explains Prof. Dr. Gabriel Schaaf, member of the PhenoRob Cluster of Excellence from INRES Plant Nutrition.
The study falls within the scope of basic research, but also opens important possibilities for plant breeding. "Improved understanding of the genetic and molecular function of nitrogen sensing will accelerate the breeding of varieties with improved nitrogen use efficiency," Ballvora says, looking to the future. However, this would require a better understanding of the individual steps in the signal cascade of the NPF2.12 sensor that result in stronger root growth under nitrogen deficiency.
Participating institutions:
The Plant Breeding and Plant Nutrition groups at the Institute of Crop Sciences and Resource Conservation (INRES) and the research campus Klein-Altendorf of the University of Bonn were involved in the study, as were the Institute of Quantitative Genetics and Genomics of Plants and the Cluster of Excellence Plant Sciences CEPLAS at the University of Düsseldorf.
If nitrogen levels in the soil are low, wheat varieties with a favorable NPF2.12 gene variant (left) initiate an important signaling cascade: Nitric oxide (NO), an important second messenger, stimulates root growth. This increases the supply of nitrogen and the plant thrives better overall. Without this preferred NPF2.12 gene variant, the plants (right) remain small and stunted under these conditions.
CREDIT
© Md. Nurealam Siddiqui
JOURNAL
New Phytologist
ARTICLE TITLE
Convergently selected NPF2.12 coordinates root growth and nitrogen use efficiency in wheat and barley
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