Winter Awakens Spring Flowering

Rick Amasino
Photo by Frederic Bouche

It’s springtime in Wisconsin again. Home gardeners and farmers are busy tending to their beds and fields, relishing the fresh sprouts of flowers, vegetables, and crops. It begs the question: What happens in the inner workings of plants as they prepare for spring? What’s the science that governs the growing season for different flora?

Rick Amasino, a plant biochemist and professor in the Department of Biochemistry, may have the answers — or at least some of them. He studies plant development and, specifically, how and when plants produce flowers. In 2016, his expertise earned him a place on a National Academies of Sciences, Engineering, and Medicine committee tasked with investigating the impacts of genetically engineered crops.

Many plants have effectively evolved a way to avoid flowering prior to winter. Instead, they use the cold season to help activate flowering when the weather warms. Amasino’s research sheds light on what conditions a plant must experience in order to flower. In particular, he focuses on unraveling the genetic basis of the effects these conditions have on plants as they stimulate or repress flowering. His findings may allow other scientists and plant breeders to develop crops that are more efficient and have higher yields of food or energy.

How do plants respond to spring?

There are a wide range of responses. For example, some plants need to be exposed to winter cold to flower in the spring, whereas others form spring flowers as a result of being exposed to the decreasing hours of sunlight during the fall season. Apple and cherry trees are in this latter category — their flowers are actually formed in the previous fall in buds that become dormant. Then, when it gets warm the following spring, everything that was crammed into those buds in the fall just unfolds. Other plants like lilies, for example, require exposure to cold in order to flower. When they are growing in the fall, flowering is blocked. But over winter, the block is removed and they flower in the spring. The underlying processes for this involve a lot of biochemistry, and that’s what we’ve studied in my lab. Specifically, we study how flowering is blocked in the fall and how exposure to cold results in the removal of this block. The block removal process is known as vernalization; this word is derived from vernal, which means “relating to spring.”

Are there any more examples of plants that need winter to flower?

Some common examples include many of the vegetables we plant in the spring, such as cabbage, carrots, and beets. We don’t usually see these particular vegetables flowering because they will not flower until they experience winter, and we harvest them before they have a chance to flower. Many grasses go through this process as well.

Why should we be interested in this process?

This requirement to go through winter in order to flower is important agriculturally; food plants keep growing without flowering all summer long and, therefore, the part which we consume can get very large. However, if you left a carrot in the ground after the summer, it would flower the next spring, and the underground part of the carrot we eat would become shriveled as it provides the nutrients for flowers to form.

If it gets warmer earlier, is that a problem?

An early warming trend in itself isn’t problematic if it continues into spring, but our climate is likely to be more variable than that. So, if we have unusually high temperatures late in the winter and cherry blossoms in Door County open, but then we get a blast of cold afterward, the flowers will be destroyed and fruit cannot form.

What’s going on on the inside of the plant that determines whether or not it flowers?

In the plants we study that require winter, there is a gene encoding a repressor protein that is expressed in the fall that prevents the plant from flowering. Then, over the winter, control of the repressor gene is altered in a way that the repressor is no longer expressed. Consequently, plants can flower when it gets warm, and they resume growth in the spring in the absence of the repressor protein. We’ve recently published research specifically on the small Mediterranean grass called Brachypodium. Previous work has shown that a gene called VRN1 is responsible for activating flowering in these grasses after the winter. But what’s the repressor gene keeping VRN1 in check in the fall? That was previously unclear. We did genetic screens and found several of the genes that repress the VRN1 gene prior to winter. We just published a scientific paper on one of these, calling it RVR1, for its role in repressing VRN1.

Why are gene discoveries like this important for this area of research?

Scientists that breed cereal grains may find this newly identified gene interesting. However, we think it could also impact biofuels research. I am part of the U.S. Department of Energy’s Great Lakes Bioenergy Research Center (GLBRC) here on campus. Although switchgrass, which can be used to make biofuels, doesn’t go through the vernalization process, there’s a good chance that taking the RVR1 gene from Brachypodium and putting it in switchgrass will delay switchgrass flowering. Delaying switchgrass flowering to various extents may improve yield.

Why is understanding this process important?

In basic research like ours, we often don’t know where exactly it’s going, but it often ends up having practical relevance. Our goal is to understand the biochemical pathways that plants have evolved to flower at certain times of the year. But in crops, in which the timing of flowering is important, this research can be applicable. For example, we share our unpublished work with wheat breeders who can translate some of the knowledge into increased efficiency in a breeding program. Also, our work has revealed basic principles of how genes are regulated, which has implications for many areas. Another example of applicability, although not directly from our research, was useful for sugar beet farmers, who plant in the spring. A spring cold spell will trigger some of the sugar beets to flower, and flowering plants do not produce the part of the beet the farmers harvest. Scientists in Europe modified genes involved in the flowering response to cold and came up with a sugar beet variety that doesn’t flower if it is exposed to cold. Now farmers can plant their beets in the fall rather than the spring to allow them to have a much longer growing season and to grow bigger — and they don’t have to worry about the beets flowering. This has significantly increased the yield per acre of sugar beets.

What’s your next step in this research?

We are going to continue to work with other GLBRC researchers to study Brachypodium and how different varieties of the plant live and persist in winters that have varying temperatures and lengths. How did one variety evolve a system tweaked to require 16 weeks of cold? Why does another one require just two weeks of cold? In other words, what’s the genetic and biochemical difference between the requirement for a short winter versus a long winter? Grasses are really important crops, and this model for studying flowering can tell us a lot about how they work

Kernza: Perennial Crop with Perks

Valentin Picasso’s career has taken him across two continents — and always from the ground up. His research as an assistant professor in the Department of Agronomy focuses on forage and grazing systems in the United States and around the world.

A native of Uruguay, Picasso earned his Ph.D. in sustainable agriculture from Iowa State University before returning home to teach for seven years at the University of Uruguay (UDELAR). Now back in the Midwest, he is intrigued by the ways sustainable agricultural methods, such as the use of perennial crops (those that can be harvested year after year), can build resilience to worldwide threats like climate change. Because perennials have deep roots, they hold soil in place, reduce water contamination, and rebound quicker from drought or extreme temperatures.

One such crop is Kernza, which was developed through selective breeding of a Eurasian forage grass related to wheat. In addition to its use as feed for livestock and its environmental benefits, it also serves as a grain crop, weed fighter, and money saver, all of which is boosting its popularity among farmers.

Picasso is excited to collaborate with his new colleagues at UW–Madison. “There are lots of opportunities to develop interdisciplinary projects to solve the most critical problems we are facing today in terms of agricultural sustainability,” he says.

And in an era of increasing globalization, Picasso has cast his gaze beyond the borders of Wisconsin. He maintains an international focus as he studies the agroecological intensification of grazing systems around the globe, especially in Latin America.

You’re working with Kernza. Can you tell us what that is?

Kernza is a perennial grain and forage crop, so it is a dualpurpose crop. You can harvest grain out of it, and you can harvest forage out of it. Once you plant it, you can harvest it for many years. The grain can be used as human food, just like wheat; you can use it for flour for making bread. You can ferment it and produce beer or other drinks. We’re also looking at weed management. This crop has the potential to really clean a field of weeds because it’s really competitive. Once it is established, it outcompetes a lot of weeds.

Where does it come from?

This plant is originally from central Europe and Asia. It was introduced as a forage crop to the U.S. in the early 1900s, and it’s been bred over the last 10 years by The Land Institute in Kansas. When you think about this, the breeding for grain of this crop started only 10 years ago. The breeding for grain for other crops started thousands of years ago and have been in modern breeding for hundreds of years.

And here in Wisconsin, which people are interested in Kernza?

The main interest here in Wisconsin comes from farmers who want to have a flexible crop that they can use for harvest grain, but at the same time they may have some dairy or beef — farmers who have cattle and want to be able to harvest forage or to graze this crop. So, we’re doing research on what the impact of grazing is on the grain production. You can either graze it in the spring or graze it in the fall, before or after the grain harvest. So, it produces a lot of forage and a lot of biomass, but at the same time you can harvest grain, which is what everybody wants.

How long will it last when it’s planted?

A crop of intermediate wheatgrass can last a long time. You can have it for 10 or 20 years. The grain production in the first two years is usually very good and then declines in the third year. We’re trying to understand why this happens. Every time we talk to farmers, they’re very interested in trying it both for forage and for grain. It would fit very nicely here in Wisconsin because we’re a dairy state, and dairy farmers have that unique set of skills as grain and livestock farmers. So that’s exactly what we need.

Is there any need for special equipment or agronomic practices?

Well, this is basically a forage grass, so anybody with machinery to plant forage grass can plant it. For harvesting, you can use a small grain combine. So, it’s just normal agricultural practices. The main issue now is the learning curve for farmers because every new crop requires learning new methods.

What is the market for the grain?

There’s a lot of interest right now in that grain. For instance, there’s Patagonia Provisions, which is a food company that has just produced what they call “Long Root Ale,” which is basically a beer brewed out of 15 percent Kernza grain. Recently, General Mills also announced that they are going to incorporate this perennial grain into some of their products in their organic Cascade Farms brand. And then there are a lot of restaurants and bakeries in the area where they are serving products with Kernza as part of their menu or as part of their baked goods.

So a farmer can market this grain if they grow it?

Absolutely. There’s a large demand for that. There’s a group called Plovgh [in Viroqua, Wisconsin] that a farmer should contact if they’re interested in growing Kernza, and they can provide the seed and the basic knowledge how to manage this crop in order to get a harvest. We’re very confident that the grain yields will increase. Because this is a new crop, there’s a lot of agronomic management issues that we haven’t figured out yet. What’s the proper harvesting method? What’s the proper harvesting time? What machine works best? What are the settings of the combine? All of these are things we’re still learning. And that’s what makes this really exciting. The research we’re doing, everything we learn makes a change in the way farmers can manage the crop, so that’s really exciting. And, really, commercial production started two years ago.

Any recommendations for a farmer who might want to try this?

The main thing is to start small. We recommend farmers try it in a small area and get familiar with the crop before deciding to go to larger acres. Ideally, we’re looking for farmers who are familiar with growing grains. But at the same time, it’s great if you have cattle. That way, you can either graze it or harvest the hay and give it to the cattle, and that’s what makes it profitable right now — the dual use. Dairy farmers who are very used to harvesting grain and have cattle are clearly a good target for this grain.

At what point can we expect perennial grain crops to be as productive as annual grain crops?

Yields of Kernza have been increasing rapidly and continue to grow. Kernza grain yields are between 400 and 900 pounds per acre in the first year. However, the productivity of Kernza is measured not only in terms of grain yield but also in terms of forage yield. Kernza can produce up to 5 tons per acre of forage on top of the grain yield, which can be grazed or hayed. And inputs like fertilizers, pesticides, and machinery passes are minimal, so costs are much lower than annual crops.

What are the other advantages to Kernza?

The main advantage of growing this perennial grain is the environmental benefits. Because it’s perennial, it covers the ground year-round for many years, so there’s no soil erosion, there’s no leaching of nutrients into the groundwater. It’s a great way of conserving soil and water quality. It also has very deep roots, so the amount of carbon that it can fix in the soil is important. In a way, it’s also reducing greenhouse gas emissions and climate change. The main reason you would want to develop this are the environmental benefits.

The Secret Lives of Bacteria

CONSIDERING HOW WELL STUDIED THEY ARE, SOME LARGE GAPS remain in our scientific understanding of bacteria. For instance, we don’t yet know how bacterial chromosomes are separated into daughter cells during cell division or how their complicated chemical language really works. Using techniques from a broad spectrum of fields—including biochemistry, genetics, materials science and engineering—biochemistry professor Doug Weibel is designing advanced microtools and novel experimental setups to answer, for the first time, persisting questions about these surprisingly complex microorganisms. Through this basic work, he’s finding novel antibiotics and other interesting drug candidates.

Why are there still so many major unknowns about bacteria? How can that be?

The issue with bacteria is they are so small. By comparison, eukaryotic cells are enormous! For a calibration point, a human hair is about 100 microns in diameter. That’s about the thickness of a piece of scotch tape. And a eukaryote—when it’s spread on a surface—is maybe 40 microns in diameter. But the bacteria we look at are about one micron long, and their short axis is just several hundred nanometers. Until recently it was very difficult to look at them under a microscope and see anything useful going on inside the cell. Fortunately, there’s been a revolution in optical microscopy techniques over the last five years, and now we can see inside them with pretty good resolution.

How has our understanding about these microorganisms grown in recent years?

Historically, bacteria have always been thought of in the context of the way that we studied them: as individuals. They were always freely suspended in liquid nutrients and were dilute enough so that they never made physical contact with each other. But it’s pretty clear now that many bacteria in the ecosystem exist in tight-knit communities.

And during certain developmental stages, bacterial cells will display collective dynamics, where they are no longer acting as individual cells—as little one-bit processors—but are actually making collective decisions. In these cases, they are communicating and acting more like a multicellular organism—as something a lot more sophisticated than we’ve ever really appreciated.

Tell me more about this collective behavior.

A lot of people know that bacteria swim in solution, but they also swim in groups on surfaces. This collective movement on surfaces is called swarming.

As the bacterial community moves across a surface, the cells mix—and this mixing ensures that all of the cells get nutrients and growth factors to continue replicating. Swarming allows the cells to grow explosively and to colonize whatever niche they’re provided with.

What are you trying to learn about swarming in your lab?

We’re trying to figure out two things. One has to do with behavior: How does the motion of individual cells on a small scale lead to the pattern formation—the continuous mixing—of the swarm on a large scale? The other question is really the biochemistry of how it works. How do cells sense the surface and then change their morphology to interact with it?

This work should tell us some basic rules about how cells sense things outside of themselves—from fluids to surfaces to other cells. I think this is super interesting.

Many bacteria in the ecosystem exist in tight-knit communities.

Can you describe one of the microtools you’ve developed to study bacteria?

Sure, but let me give you some more context first. In addition to studying the physical interactions between bacteria during swarming, we’re also interested in the role that chemical communication plays in the development of swarms. And swarming is just an early stage of biofilm development, so we are also interested in biofilms, which are basically bacterial communities that are firmly attached to surfaces.
One question that’s been in the field for a long time is, what is the length scale over which these chemical signals can be propagated? That is, if you have a swarm or a small early-stage biofilm that’s secreting signals, how far away does another biofilm have to be before it can no longer eavesdrop? To answer this question we created a microtool that we call the waffle.