Biologists study enzymes that help wheat to fight fungi

March 11, 2019, Sechenov University
Credit: CC0 Public Domain

Scientists from I.M. Sechenov First Moscow State Medical University together with their Russian colleagues studied the reaction of wheat plants to damage caused by pathogenic fungi. They examined the activation of enzymes involved in cell death induced in response to infection. The research results and enzyme classification were published in the International Journal of Molecular Sciences.

Plant resistance to harmful microorganisms (pathogens) is largely determined by a set of enzymes encoded in DNA, which are involved in death of infected cells and prevent infection spreading. Such enzymes that provide protein breakdown are called proteases.

Despite the importance of in agriculture and science, including biotechnology, reaction of these plants to pathogens is described only in general (for example, in these two papers), without focusing on specific proteins. The complexity of the study refers to the fact that wheat, like most other plants, is polyploid. It means that each cell has several sets of chromosomes. In the case of wheat, it is attributed to the fact that Tríticum aestívum (wheat species used in agriculture) were cultivated by crossbreeding of Triticum Urartu, Aegilops tauschii and related species. As a result, the wheat genome is complex and contains 107,000 genes—that is, almost five times more than a human genome.

Wheat is exposed to various pathogens (bacteria, viruses, fungi), nematodes (roundworms) and insects. Some of them parasitize on living plant cells, slowing their growth (biotrophic pathogens), others feed on cell content that leads to its death (necrotrophic pathogens).

The scientists used two pathogens: a biotrophic pathogen (Puccinia recondita), that causes wheat leaf rust, and a necrotrophic pathogen (Stagonospora nodorum) that damages leaves, heads and grains. The biologists studied 'Khakasskaya' and 'Daria' wheat cultivars to find out the impact of fungi infectionon plants. They used a specific method that combines and mass spectroscopy. Liquid chromatography is a technique used to identify a mixture of substances passing in a liquid flow through a tube filled with sorbent. Due to the fact that substances are absorbed in varying degrees, the mixture is divided into components. Mass spectrometry is a technique that ionizes neutral atoms and molecules into charged ions based on their mass-to-charge ratio. This makes it possible to accurately determine even complex organic compounds.

In total, the scientists discovered 1,544 enzymes that belong to five catalytic types of proteases: serine, cysteine, aspartic, threonine and metalloproteases. They determined that protease proportion common in different plant cultivars is lower than expected (about 60% vs. 79.3%). However, the differences (about 40%) are divided almost equally between several types of proteases, indicating that these enzymes are likely to substitute each other.

The study of proteases helped to predict specific sites in their structures. The process of hydrolysis in such regions may be activated in the course of proteolytic cascades. This chain reaction allows an organism to activate many enzymes quickly that help it to fight infection.

"We have discovered above all that activation of proteases found in infected plants does not involve enzymes with caspase-like or metacaspase-like activities. Although earlier it was assumed that such proteases initiate proteolytic cascade activation, that leads to cell death of the plant organism. We concluded that some other unique proteases might be involved in wheat early response to infection with both biotrophic and necrotrophic pathogens. Surely, this result should be confirmed experimentally using alternative methods," told Prof. Andrey Zamyatnin, Director of the Institute of Molecular Medicine (Sechenov University), co-author of the article.

The detailed study of enzymes allowed to clarify their classification. The scientists have described homologs (the most similar proteins) for enzymes of several groups, and clarified position of these enzymes in a phylogenetic tree (it shows evolutionary distances between proteins). For example, scientists have determined that aspartate proteases that belong to different types differ to such an extent that they may not be related, but have acquired similar functions independently.

The study also helped to clarify ideas about specific mechanisms for triggering cell death in plants. It is known that one of the main apoptosis regulators in animals are caspases—proteolytic enzymes that initiate destruction of the cells into separate elements. Some animal caspases introduce cleavages in others, and thereby send a signal that it is time to start cell death.

"The discovery of programmed cell death commonly called apoptosis (in Greek 'falling off') was not only awarded by the Nobel prize, but also determined the scientific agenda of a significant number of research teams for many decades to come. At the turn of the century, it became clear that, despite the phenomenon of programmed cell death, plants do not have caspases. However, it was discovered that have other enzymes with caspase-like activities. Most likely, they just like in animals execute cell death processes in plant . However, our study has showed that among death activators in wheat there are enzymes that do not have caspase-like activities. It confirms once more the existence of different mechanisms of programmed across eukaryotic organisms", concluded Prof. Zamyatnin.

Explore further: Newly discovered enzyme is 'firing pin' for plant immunity

More information: Anastasia Balakireva et al, Proteomics Analysis Reveals That Caspase-Like and Metacaspase-Like Activities Are Dispensable for Activation of Proteases Involved in Early Response to Biotic Stress in Triticum aestivum L., International Journal of Molecular Sciences (2018). DOI: 10.3390/ijms19123991

Related Stories

Newly discovered enzyme is 'firing pin' for plant immunity

September 17, 2018

Just like humans, plants have an immune system that helps them fight off infections. Plant immunity has some important differences: they don't make antibodies and can't fight off the same bug more quickly months or years ...

How protein modifications influence apoptosis

March 21, 2017

Researchers at the Lomonosov Moscow State University have described the molecular mechanisms of post-translational modifications of caspases, a family of proteolytic enzymes, and how they function during apoptosis, the process ...

Plants share defensive proteins in evolutionary pick 'n' mix

March 5, 2018

The recent research, led by the Krasileva Group of Earlham Institute and The Sainsbury Laboratory, used phylogenetics (the study of how DNA sequences are related) to identify how these 'bait' genes are distributed throughout ...

Recommended for you

Coffee-based colloids for direct solar absorption

March 22, 2019

Solar energy is one of the most promising resources to help reduce fossil fuel consumption and mitigate greenhouse gas emissions to power a sustainable future. Devices presently in use to convert solar energy into thermal ...

Paleontologists report world's biggest Tyrannosaurus rex

March 22, 2019

University of Alberta paleontologists have just reported the world's biggest Tyrannosaurus rex and the largest dinosaur skeleton ever found in Canada. The 13-metre-long T. rex, nicknamed "Scotty," lived in prehistoric Saskatchewan ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.