Unstable winters mean that winter cereal crops may need to time their spring flowering more according to day length and less according to winter cold in the future. Fortunately, this trait is already embedded in the plants’ genetics.
New research from the Norwegian University of Life Sciences (NMBU) shows that plants’ relationship with the seasons is more complex than previously believed. During winter, they do not simply count cold temperatures, but also track hours of light and darkness. In scientific terminology, this process is known as vernalization.
Plants in temperate cold regions must ensure pollination, development, and seed production within a very short period of favorable growing conditions during spring and summer. They control their flowering time through a vernalization mechanism that prevents flowering before winter has ended. However, increasingly unstable winters, with intermittent warm periods, can disrupt the plant’s flowering schedule.
“If winter is not cold and long enough, the vernalization effect in the plant may be weakened. This can cause flowering to begin too late, or in some cases too early,” explains Marian Schubert, researcher and molecular biologist at NMBU.
Lower yields in winter cereals
Flowering at the right time is essential for cereal crops, which are actually species of grasses. As climate change has extended the growing season, it has become increasingly attractive for farmers to cultivate winter cereal varieties. These crops are sown in autumn, germinate and establish a plant cover before winter, and then resume growth when spring arrives. This gives the plants more time to establish themselves, develop stronger root systems, and achieve higher yield potential.
However, these winter varieties must undergo vernalization before they can flower the following year. In current cereal varieties, a stable cold winter is the primary source of the vernalization signals that plants rely on. As such winters become less predictable, the result may be reduced yields.
This has renewed researchers’ interest in a little-known plant trait: the ability to respond to day length, a factor unaffected by climate change.
The concept is not new. Research conducted at the Norwegian Agricultural College in the 1980s described grass species capable of inducing flowering in response to short day lengths, a phenomenon known as short-day vernalization. At the time, however, it was considered rare, relatively unimportant, and limited to a few species.
Renewed interest in day length
Aware that this trait could become increasingly important in the future, Schubert and NMBU professor Siri Fjellheim set out to investigate a large group of grass species within the Pooideae subfamily of temperate grasses. This group includes cereal crops commonly grown in Norway, such as wheat, barley, oats, and rye. The results were surprising.
“We expected to find only a few species that responded to short days, but the results showed that the phenomenon is much more widespread than we had anticipated,” says Schubert.
The trait appears to have evolved early in the evolutionary history of this plant group as it adapted to temperate regions in northern climates. It has likely played an important role in the ability of these grasses to survive and reproduce in cool environments.
Testing the effect of day length in greenhouse experiments
A greenhouse experiment was conducted after seeds first received a cold treatment to simulate winter conditions. The plants were then grown for two weeks at approximately 20°C under long-day conditions (16 hours of light per day).
The plants were subsequently divided into two groups and grown for an additional 59 days. One group remained under long-day conditions, while the other was exposed to short-day conditions (8 hours of light per day). Afterward, all plants were returned to long-day conditions.
To determine whether exposure to short days prepared the plants for flowering, researchers measured how quickly flowering occurred and how many plants began to flower.
Gene activity revealed the plants' readiness to flower
Unlike researchers in the 1980s, Schubert and her colleagues were now able to identify genes involved in short-day vernalization.
Their goal was to determine which genes become active, or are switched “on,” when plants are exposed to short and long days. Plants regulate which genes are turned on and off. When a gene is on, it is used to produce something the cell needs; when it is off, it remains inactive. This enables cells with identical DNA to perform different tasks.
The researchers collected leaf samples and measured the activity of many genes simultaneously using RNA analyses. Comparing gene activity between the two groups revealed 93 genes whose activity changed in response to differences in day length.
To better understand how these genes worked together, the researchers grouped genes showing similar behavior. Many of these genes were shared across numerous species in the experiment and appear to cooperate in controlling when plants begin preparing for flowering.
The researchers also identified the function of an important gene, GF14h, by using gene editing to disable it and observe the consequences. By comparing the edited plants with normal plants, they found that the gene acts as a brake on flowering.
“Under the longer days of summer, this gene suppresses the reproductive process. As the days become shorter, the gene becomes less active, triggering a chain reaction that activates other genes,” says Schubert.
Stable day lengths provide new opportunities in unstable winters
The findings represent a major breakthrough in understanding the short-day vernalization process in plants.
As winters become increasingly unstable in the future, there is a real risk that yields of winter cereals will decline due to insufficient vernalization. This makes it necessary to actively incorporate short-day vernalization into the breeding of new cereal varieties, since day length itself is unaffected by climate change.
By applying this new knowledge of the genes that control responses to short days, plant breeders can develop crops that are better adapted to future climatic conditions.
“We have now developed an overarching model for the Pooideae subfamily, but we only examined one population of each species, so the full picture is actually much more complex. Barley was included in the study as a species, but there are thousands of barley varieties cultivated across temperate regions,” says Schubert.
Using the model, plant breeders can identify and analyze these genes in different varieties and map the gene variants present in the barley cultivars most widely grown in Europe.
This research has significant implications for agriculture by helping winter cereal crops adapt to climate change. It also provides insight into how wild plant species may adjust to changing environmental conditions. Species equipped with both temperature-based and day-length-based mechanisms have a better chance of survival. Unlike cultivated crops, however, wild plants must rely on natural selection, or “survival of the fittest,” rather than assistance from plant breeders and researchers.
Referance:
Conservation of the short-day vernalization flowering response pathway in tempeMarian Schubert, Marian Schubert mfl.: Conservation of the short-day vernalization flowering response pathway in temperate Pooideae grasses. New Phytologist, 2026. Doi.org/10.1111/nph.71009