Faculty Focus: Scientist Studies Time’s Essence in Plants

NC State's Dr. Colleen Doherty studies the circadian rhythm of plants. Among the projects she's involved with: finding ways to make hops plants more suitable for North Carolina day length.

NC State's Dr. Colleen Doherty studies the circadian rhythm of plants. Among the projects she's involved with: finding ways to make hops plants more suitable for North Carolina day length.

It’s often said that time is of the essence, and now, thanks to the work of NC State University’s Dr. Colleen Doherty, we are learning more about how true that is for plants.

Doherty, an assistant professor in NC State University’s Department of Molecular and Structural Biochemistry, explores plants’ molecular signaling networks and how changes in these networks over the course of the day affect plants’ response to heat, drought and related stresses.

What she’s finding has important implications for agriculture, as she explained in a recent ‘CALS Faculty Focus’ interview.

You study the circadian rhythm of plants. What does that mean?

As you know, we have internal body clocks that affect our digestion, our cognitive abilities and other functions, and we become particularly aware of our body clock when it’s not in synch with our environment: when we experience jet lag, for example, or when we change to daylight savings time.

One of the things that body clocks can do is to anticipate recurring events. If you eat breakfast every morning, your body anticipates that and may start growling when you wake up.

Just like humans, plants also integrate the time of day with their environmental processes and they anticipate recurring events in their lives. For example, just before the sun comes up, plants start doing photosynthesis. They are prepared. They are ready to catch the very first light of dawn. They have their all their photosynthetic machinery up and going before the first light even hits.

We are particularly interested in how this anticipation, this synching of the body clock with the environment, is involved in response to abiotic stresses — so stresses that are caused by environmental changes such as heat or drought or low temperatures.

What kinds of questions are you exploring?

One of the main things we are focused on is the influence of high nighttime temperatures. We know that plants have a hard time adjusting to high temperatures, but it turns out that the time of day that the plants get those temperatures makes a difference: If plants get hot in the middle of the day, they can handle that. But if they get a little bit of a temperature increase at night, when they don’t expect it, it can be much more damaging than a large temperature increase during the day.

This is important because, with climate change, one of the observed features is that nights are getting warmer faster than days. We are talking about a very small increase, but still the nights are getting warmer at a faster rate than days are.

So this upsets the plants’ balance, because they’ve learned over the last million years to anticipate a certain temperature at night, depending on the crop plant. But we don’t know if there’s a specific [biochemical] pathway that makes the plants more tolerant to higher daytime temperatures or more vulnerable to higher nighttime temperatures. And that’s what we work on.

Why is such an understanding important to agriculture?

If heat stress is worse at 2 a.m. than it is at 2 p.m., then understanding what’s going on in the plant at different times of the day could help us find plants or mechanisms of management that would allow us to improve tolerance to heat stress. For example, can we find out what pathway regulates the plants’ response during the day and get the plant to turn it on at night?

What led you to this type of research?

I went to undergraduate at the University of Southern Indiana. I was a communications major the first time around, and I worked as a vet tech for many years in an emergency clinic. I loved that and was actually going back to school to study veterinary medicine … but I had a professor who encouraged me to apply to both graduate school and vet school. So I did. … And when I went to the grad school interviews, people were talking about exciting stuff, and I felt, ‘This is where I belong.’ …

I wasn’t convinced I wanted to work on plants then, but I went to grad school at Michigan State, where they did this neat thing where there are 180 labs you can join and each of the professors gives a talk about what goes on in the lab. I just found that I was so excited and interested in the ones related to plants, because there is so much we don’t know about them.

I ended up in grad school studying low-temperature tolerance, and I realized that the time of day they were getting the stress really makes a big difference. I decided I needed to understand the circadian clock if I wanted to be able to work on abiotic stress at all. Time is just such an important overall part of plants, just as it is with humans. I did my post doc at a lab that specializes in the circadian clock. That was at the University of California-San Diego. … From there, I came to NC State.

Anything else you’d like to share?

We have another project that I am quite excited about: We work on trying to make hops — the stuff that makes your beer taste good — grow better in North Carolina. Everybody wants to start growing hops now to feed the local beer industry, which is exploding.

And with hops production, timing is important: Hops are typically grown in the Pacific Northwest, so it’s further north, where there are longer days. When the plants come out in the spring, there’s a certain amount of time before they are fully mature. They won’t flower all summer when the day length is longer than 15 hours — they’ll just keep getting bushier and bushier and bigger and bigger. Then when the day length gets to be less than 15 hours, they flower very suddenly and the yield is high.

Here in North Carolina, the days don’t get longer than 15 hours really almost the whole summer, so once the plants mature, they are never inhibited from flowering. They go straight to flowering and don’t get big and bushy with a lot of branching, so the yield is much less.

It also causes another problem — instead of having all the harvest at once, … you have to harvest little pieces here and there, by hand. So that makes hops production here much more expensive.

As humans, we have selected crops for different photoperiods from ancient times. So as people migrated around, they took long-day plants made them short-day, and vice versa we have switched crops back and forth: rice, sorghum, peas and almost any crop you can think of. … When you go back at look what was selected for, it’s almost always clock genes and light-sensing genes.

What we want to do is look at some of those genes and see if they are also responsible for sensing day length in hops. If so, can we now make hops more suited for North Carolina? And if we can do that, we can use those as markers to breed varieties that are more tolerant for North Carolina. So we could double our hops yield.

That’s one strategy, but the other half is that we don’t know much about the hops cone production, but the metabolites that are produced there may be daylight sensitive, as well. So if we can’t improve the timing of the hops flowering, maybe the hops cones that we get here may have a unique profile with unique metabolites that create a greater market value. So maybe the yield of North Carolina-grown hops might be less, but their market value might be higher.

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