Hey, Stress, LEAve Them Plants Alone

When the going gets tough, the tough get going.  But what happens if you are an immobile plant, trapped in one spot?  This is the challenge faced by many plants during times of drought, cold, and other stressful conditions. How do they survive?  

It turns out that plants have some very effective molecular defenses against stress. Among these defenses, is a large group of proteins known as “LEA” proteins. Because of their protective properties, LEA proteins are of great interest to plant biologists and biochemists, but one group – the LEA3 proteins – has not been well studied.

Dr. Steffen Graether, a professor in the Department of Molecular and Cellular Biology, and graduate student Karamjeet Singh are helping to change that by elucidating the structure and function of these proteins.

Graether has been researching LEA proteins since he first began working at the University of Guelph.

“I actually have to blame Dr. Annette Nassuth [a colleague in the same department] for my interest in these proteins,” says Graether. “She talked to me about LEA proteins when I interviewed. Then when I began to study them in my lab, I saw that they have no structure, but they do have a function, which goes against all the structural biology I had learned.”

Graether and Singh were interested in LEA3 proteins since previous research showed that they were located in the cell’s mitochondria, which means they may have a special role to play in protecting these critical cell organelles from stress.

But first the researchers needed to generate a large enough quantity of LEA3 proteins to run their experiments. They did this using genetically modified microbes that produce LEA plant proteins. The microbes act like a small factory, churning out the proteins of interest.   

LEA3 proteins are naturally “disordered”, which means they do not have a fixed three-dimensional structure. This led to a few bumps in the road when Graether and Singh tried to generate the proteins using bacteria.

“I very naively thought, ‘Oh, well, it’s a disordered protein and it can’t really denature [lose its structure], so it should express well in our production system.’  But that was not the case,” says Graether.

Despite these initial challenges the research team persevered and was able to express and purify the LEA3 proteins. This paved the way for the rest of their experiments.

Because LEA3 proteins are disordered, they can carry out a wide variety of protective functions. Of these many functions, Graether and Singh looked at LEA3’s capacity to bind metals, interact with membranes, and protect enzymes from cold.

Their results showed that some LEA3 proteins bind metals, which can accumulate during stress and cause damage. Other LEA3 proteins interacted with compounds that mimic cell membranes. In a living cell, such interactions would help maintain membrane integrity during the dehydration stress that accompanies drought or cold conditions. However, in freeze/thaw tests, the LEA3 proteins studied by Graether and Singh were less efficient at protecting certain plant enzymes from cold damage compared to other types of LEA proteins.

Graether believes that the disordered structure may be helpful in preventing the protein from unfolding when stressed. If the protein was folded in an ordered manner – as is the case with most other types of proteins – it could unfold at cold temperatures and lose its ability to function.

So what’s next for this research?   

Graether says, “While the work we’re doing is very informative, it’s all carried out in vitro [outside of a living thing]. It’s definitely time to look at in vivo [living] models to get some more complexity and specificity in the system.”

LEA proteins are found throughout the plant kingdom. Outside of plants, there are no other obvious LEA proteins, but there are proteins with similar sequences. One of these proteins was actually found in Antarctic shrimp.

The widespread occurrence of LEA (and similar) proteins demonstrates their important role in the natural world. Unlocking their secrets may help researchers find ways to improve stress tolerance in agricultural crops. 

But the usefulness of these proteins may extend to other unexpected places as well.  For example, they could be used as an additive to enhance the stability of high-value pharmaceuticals, especially those stored at cold temperatures.

This study was funded by the Natural Sciences and Engineering Research Council.

Read the full study in the journal Protein Science.

Read about other CBS Research Highlights.