Christmas Cactus Provides Clues to Heat Resistance in Crops

Dr. Leslie Gunatilaka first came to the University of Arizona, from the lush landscapes of Virginia, in 1996. One of his first questions was “How do desert plants tolerate such extreme heat?”. Of course plants have morphological adaptations (like small leaves to stem the amount of water lost through evapotranspiration) but he thought they also might have physiological adaptations – changes on the molecular level to protect themselves from the effects of heat.

 

All living things have a kind of protein called ‘heat shock protein’ – which help protect regular proteins from the effects of heat (or any other kind of stress – Dr. Gunatilaka is quick to point out – they would be better known as stress proteins).

 

Heat shock proteins, one of many “chaperone” proteins, exist to prevent other proteins from becoming denatured (unfolded and no longer useful to a cell). When the yolk of a fried egg solidifies you’re seeing the denaturing of proteins. If an egg were to have more heat shock proteins it would take longer for the heat to have its denaturing effect.

 

There are compounds which modulate heat shock proteins – either to increase or decrease their effectiveness. And some of these proteins are found in the fungi that grow on the roots of desert plants. Dr. Gunatilaka and his colleagues isolated a compound, called monocillin, from a fungus around the roots of a Christmas cactus which modulates the expression of heat shock proteins. The researchers ran tests to see how the compound affects gene expression in the heat shock protein. In tests on seedlings in the lab they found positive results – plants that were treated with the compound survived prolonged heat stress while untreated plants died. The experiment has been taken to the next level by an bioengineering company who has found positive results in large scale greenhouse experiments and plans to test the treatment outdoors this year.

 

Since monocillin modulates the effect of heat shock proteins, it also has an important application in cancer research. Cancer cells also grow in a stressed environment due to their rapid growth and high consumption of resources. They depend on active heat shock proteins to grow. Dr. Gunatilaka and his collaborators have also found that heat shock proteins can also be inhibited by monocillin – and has shown slowed growth and cell death in cancer cell lines treated with the compound.

The Sonoran Desert contains a wealth of adaptations for tolerance to extreme conditions – with implications in agriculture and medicine being uncovered by researchers in the School of Natural Resources & the Environment.