How plants 'muscle up' as they prep for the cold

Plants, like humans, do not like very hot or cold weather. Temperature extremes are a major factor that determines where plants grow and that can limit agricultural production.

December 7, 2017 - Author: Igor Houwat, Yong Sig Kim

Plants, like humans, do not like very hot or cold weather. Temperature extremes are a major factor that determines where plants grow and that can limit agricultural production.

For example, according to the EPA, in 2010 and 2012, high nighttime temperatures affected corn yields across the U.S. Corn Belt, and premature budding due to a warm winter caused $220 million in losses of Michigan cherries in 2012.

Since plants cannot move when the weather gets unbearable, they have evolved fascinating molecular strategies to survive.

The Thomashow lab at the MSU-DOE Plant Research Laboratory specifically focuses on how plants handle cold weather.

In their latest study, published in the journal The Plant Cell, they further our understanding on how a plant  protein, called CAMTA, helps plants fortify themselves as they anticipate long periods of cold, like, say, three to four months of winter in the American Midwest or Northern Europe.

The long-term goal behind the research is to breed or create plants with higher tolerance to wild swings in temperature, which would improve crop yield for food and bioenergy purposes.


Intersection of cold protection and bacteria defense systems

Yong Sig Kim, a post-doc in the Thomashow lab, says, “CAMTA proteins are universally found across plants, and they help turn on genes that impart freezing tolerance to these plants.”

In the new study, the scientists show that CAMTA proteins alsocontrol how plants defend against harmful bacteria, when it gets cold.

Under long-term cold conditions, plants build up high levels of  salicylic acid (SA), a compound that protects against bacteria, even if the plants aren’t under attack.

“At warm temperatures, however, CAMTA proteins block the system that produces SA. When it gets cold, long enough, an unknown signal is generated that modifies CAMTA to allow SA production to turn on.”

The scientists identified the N-terminus, the start of CAMTA proteins, as responsible for stopping SA production, under warm conditions.

In the cold, the C-terminus, the end portion, detects a signal, possibly a rise in cellular calcium levels, that enables SA to be produced.

This observation reverses current accepted models, which proposed instead that the C-terminus blocked SA production.



Why muscle up in the cold?
But how does temperature tolerance relate with defense against bacteria, in the first place?

“That is a very intriguing question. SA doesn’t protect the plant from the cold, per se. Instead, we think the plants enhance their immune systems in the cold as a general preemptive strategy.”

This is the idea: Although plants take measures to survive the cold, they still get injured, and their structures are destabilized, which makes them more vulnerable to bacterial infection.

So, weakened plants keep their guard up as a precaution, rather than waiting for an attack before activating their defenses, the latter which could be too little, too late.

It’s like how we humans take preventative measures to stay healthy: eat well, sleep eight hours, hydrate, etc. Slack off on some steps, and we likely get the sniffles.

Yong Sig concludes, “We have delved further into CAMTA and provided more evidence for its activity. Plant defense science is gradually revealing how protection mechanisms against the elements and against other living beings are seemingly interrelated.”

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