Plants, like people, have a circadian clock and they sense seasonal changes to light and temperature. Plants that bloom in the spring use the longer days and warmer temperatures as seasonal cues that it鈥檚 time to bloom.

Last December was the warmest on record for Washington, . As the mild winter continues, many of the plants in our gardens are starting to show signs of small buds, even though it’s only February.

, a 天美影视传媒 professor of biology, studies the genes that plants use to monitor seasonal changes. UW News asked Imaizumi to talk about how plants know when to bloom and whether this might change in warmer winters.

How do plants know when it’s time to bloom?

Takato Imaizumi: There are two major factors that plants use to sense the seasons: light 鈥� the presence or absence, the intensity, or the color at a specific time of day 鈥� and temperature. To control flowering time, plants sense light conditions in the leaves and temperature at shoot tips, which are buds that contain cells that allow the plant to grow and make a flower.

All plants use both factors, but some plants rely more on temperature than light. Some examples include tulips, crocus and cherry blossoms. Plants that rely more on light include mustard greens, cabbage, rapeseeds and chrysanthemum, though temperature is still important for these plants.

Other environmental factors that can affect bloom time include water and the availability of nutrients.

How do you think the warmer weather in December has affected the plants here in Washington?

TI: Temperatures will affect plant growth and development. I assume that warmer ambient temperatures will accelerate the flowering process of some plants that use temperature information to control flowering time.

How does studying the genes involved in the timing of plant flowering help with conservation biology?

TI: Proper timing of flowering is crucial for reproductive success and the health of a plant species. Understanding how the flowering genes are regulated will help us predict how future changes in climate may affect flowering times. That will give us a better sense of which plants may struggle.

This information could also help us design restoration strategies for plants that are struggling. For example, if we wanted to introduce a plant to a novel environment, we would have some ideas about what it would require to thrive. Plants are adapted to local environments. Even within the same species, a plant that lives farther north may require different light and temperature conditions to grow and flower compared to the same species growing farther south. When we think about transplanting plants for conservation, learning specific environmental requirements may increase the chance of transplant success.

For more information, contact Imaizumi at takato@uw.edu.

Knowledge of this process at the cellular level is critical for understanding how plants allocate resources and produce the components we care most about 鈥� including the grains, tubers, leaves, nuts and fruits that mean so much to humans and animals alike.

In a published Sept. 24 in the journal , an international team of researchers has discovered that the gene FT 鈥� the primary driver of the transition to flowering in plants each spring 鈥� does something unexpected in plants grown in natural environments, with implications for the artificial growing conditions scientists commonly used in the lab. The team, led by 天美影视传媒 biology professor , showed that FT has a peak of activity every morning leading up to the transition, something that scientists had not previously seen in Arabidopsis, a model plant that is widely studied for understanding the molecular details of the transition to flowering. The morning peak of FT activity causes plants to transition earlier from vegetative growth to flowering.

“Previous research on FT activity in Arabidopsis showed that there is a peak of activity in the evening, not the morning,” said Imaizumi, who is senior author on the paper. “We show definitively that there is a peak of morning activity 鈥� and we think we know why this morning peak was not seen previously in the research laboratory.”

Prior research, which saw only an evening peak of FT gene activity, had been conducted on Arabidopsis plants grown indoors under fluorescent light. Imaizumi and his team 鈥� which includes researchers in Switzerland, Scotland, South Korea and Japan 鈥� grew their plants outside under sunlight.

Imaizumi wanted to do this experiment because conditions at the summer solstice in Seattle, where his lab is located, are similar to the standardized, artificial “long-day” growing conditions for Arabidopsis: 16 hours of light and eight hours of darkness.

“I always wanted to grow plants outdoors in conditions similar to the lab just to make sure that what we’re seeing in lab with Arabidopsis is really what’s happening in nature,” said Imaizumi.

His team grew non-transgenic Arabidopsis plants outdoors for five consecutive summers and compared them to plants grown indoors under artificial long-day conditions. Outdoor plants produced fewer leaves than indoor plants, indicating that the outdoor plants flowered earlier. Both outdoor and indoor plants showed evening peaks of FT gene activity, but outdoor-grown plants also showed a morning peak of FT activity. They concluded that the indoor, artificial growing conditions missed key qualities of natural conditions, throwing off expression of the FT gene and the trait it governs. When active, the FT gene produces a protein that travels from the leaves to the shoot apical meristem 鈥� the niche of stem cells in the shoot that produces above-ground growth 鈥� and switches the meristem from vegetative growth to floral growth.

To identify the differences between indoor and outdoor growing conditions, Imaizumi’s group focused on light. The fluorescent bulbs commonly used in Arabidopsis research do not emit the same wavelengths of light that sunlight does. Fluorescent bulbs, for example, generate less light from far-red wavelengths. In the outdoor growing plots, the ratio of red-wavelength light to far-red wavelength was about 1-to-1, but for fluorescent bulbs this ratio is higher than 2, which means they emit more red light than far-red. When the researchers added a far-red LED lamp to the indoor growth chambers to mimic outside light, the Arabidopsis plants then showed a morning peak of FT gene activity.

In addition, by modifying the temperatures in the indoor growth chambers to cycle daily from about 16 degrees Celsius to almost 23 C 鈥� or from 61 degrees Fahrenheit to about 73 F 鈥� the evening FT gene activity was reduced, similar to the outdoor plants.

FT has been studied in other plants, including some crop plants, which also show morning peaks of FT expression. But most commercially important plants are too large or grow too slowly for the controlled-environment studies that are required to determine the cellular and genetic details of plant traits. That is why Arabidopsis, a small, fast-growing weed from the mustard family, is widely used as a substitute model organism.

The team’s findings are an opportunity to revisit the artificial growing conditions, according to Imaizumi.

“Arabidopsis has been studied for decades. Researchers set up their indoor growing conditions the best they could, given equipment, time and funding, and passed those conditions down to scientists they trained,” said Imaizumi. “But we need to change those conditions so that what we find in the lab reflects nature more closely. If we see a change in flowering by making these minor alterations, I imagine that other traits will change as well.”

Critically, their results illuminate a path forward for plant researchers to adopt artificial growth conditions that more accurately reflect natural growing conditions.

“We show that just a few simple modifications are needed to the artificial growing conditions, which researchers are using worldwide, so that lab research on Arabidopsis more and other plants accurately mimics outdoor growing conditions,” said Imaizumi. “This ensures that the discoveries made in the lab will be more comparable to what the biological processes are 鈥� at the cellular and molecular level 鈥� in other plants of interest in nature.”

Co-lead authors on the paper are former UW postdoctoral researchers Young Hun Song and Akane Kubota. Song is now an assistant professor at Ajou University and Kubota is an assistant professor at the Nara Institute of Science and Technology. Co-authors are Michael Kwon, Nayoung Lee, Ella Taagen, Dianne Laboy Cintr贸n, and Nhu Nguyen at the UW; Michael Covington with Amaryllis Nucleics; Dae Yeon Hwang at Ajou University; Sarah Hodge and Andrew Millar at the University of Edinburgh; He Huang and Dmitri Nusinow at the Donald Danforth Plant Science Center; Reiko Akiyama with the University of Zurich; and Kentaro Shimizu of both the University of Zurich and Yokohama City University. The research was funded by the U.S. National Institutes of Health, the U.S. National Science Foundation, the Rural Development Administration in South Korea, the Japan Science and Technology Agency, the Japan Society for the Promotion of Science, the Swiss National Science Foundation, UK Biotechnology and Biological Sciences Research Council, and the National Research Foundation of Korea.

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For more information, contact Imaizumi at 206-543-8709 or takato@uw.edu.

DOI: 10.1038/s41477-018-0253-3

Grant numbers: GM079712, IOS-1656076, IOS-1456796, PJ013386, JPMJCR16O3, 17H04785, NRF-2015R1D1A1A01058948, BB/N012348/1, DBI-0922879.

While humans are alone in their struggle to balance work and Netflix, all creatures wrestle with proper timing. With limited resources, organisms are pressed to use time wisely in all aspects of their lives. As researchers recently discovered, this struggle even extends to something as sweet and pleasant as the fragrant scent of a garden flower.

A team of has identified a key mechanism plants use to decide when to release their floral scents to attract pollinators. Their findings, 聽by the , connect the production and release of these fragrant chemicals to the innate circadian rhythms that pulse through all life on Earth.

The researchers studied these questions in the common garden petunia. This white-flowered hybrid releases an aromatic, sweet-smelling fragrance in the evening to attract insect pollinators, such as hawk moths.

“Plants emit these scents when they want to attract their pollinators,” said , UW associate professor of biology and senior author on the paper. “It makes sense that they should time this with when the pollinators will be around.”

discovered a major gene that controls when the petunia releases its fragrance. The gene 鈥� known by its acronym LHY 鈥� is found in many plant species and is a key component of the plant “circadian clock.”

Biologists have long recognized that creatures like plants, humans and even tiny bacteria all have circadian clocks 鈥� genes that keep their cells synchronized to the 24-hour cycle of life on Earth. These genes regulate cellular activities based on the time of day. Researchers had previously shown that LHY is a component of the circadian clock in other flowering plants, but this week’s paper marks the first time biologists have connected LHY activity to flower scent.

“Now we’re finding out what the bridge is between the circadian clock and scent production and release,” said , a UW doctoral student in biology and one of three lead authors on the paper.

Since no one had ever studied the LHY gene in petunias, Fenske and his fellow researchers gathered basic information about LHY to show that it has the same circadian functions as it does in other plant species. Many circadian clock genes are only active at specific times of the day, when they influence the activity of other genes that control what cells are doing. The researchers in Imaizumi’s lab discovered that the petunia LHY gene is most active in the morning, at the opposite time of day when the petunia releases its fragrant evening scent.

Imaizumi and his team hypothesized that LHY’s morning activity might repress the production of scented chemicals. When they prolonged LHY’s activity into the evening, the petunias didn’t release their fragrant chemicals at all.

“That was perfect,” said Imaizumi. “It is exactly what I would hope to see.”

If LHY’s activity truly did have a negative effect on scent production, then petunia plants that lacked the LHY gene’s burst of morning activity might produce and release their scents earlier in the day. Fenske and his colleagues created petunia plants with reduced LHY activity. Those plants produced and released fragrant chemicals four to eight hours earlier in the day.

Imaizumi’s team even discovered how LHY represses floral scent production. It interferes with the activity of ODO1, another petunia gene that promotes the production and release of floral scents. By repressing ODO1 activity early in the day, LHY stops the floral scent assembly line in its tracks. When the LHY gene becomes less active later in the day, ODO1 is able to ramp up production of the fragrant chemicals just in time for the evening aromatic release.

Since genes like LHY and ODO1 are present in most 鈥� if not all 鈥� flowering plants, Imaizumi and his team believe that the interactions between these two genes may be a common mechanism for a plant’s circadian clock to influence or control the production of fragrant floral scents. If so, then changes to the strength or timing of the LHY-ODO1 bridge may explain how flowers change the timing of scent production as they evolve.

Imaizumi and his team are now testing if pollinators have a preference between normal garden petunias or petunias with altered LHY activity. In time, these experiments may pave the way for scientists to improve the pollination efficiency of other plants, including important crop species.

“We think you can really change a plant’s success by changing these cues,” said Imaizumi.

The entire team was made up of researchers from the UW biology department. Fenske’s fellow lead authors were technician Kristen Hewett Hazelton and undergraduate Andrew Hempton. Other authors included postdoctoral researcher , undergraduate Breanne Yamamoto and assistant professor of biology .

This research was funded by the National Institutes of Health (GM079712 and T32GM007270) and the National Science Foundation (IOS-1354159).

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For more information, contact Imaizumi at 206-543-8709 or takato@uw.edu.