University of Nebraska–Lincoln

Awards: Faculty

LINCOLN, Neb. — A University of Nebraska-Lincoln plant scientist's discovery of a previously unknown component in plants' immune systems provides new clues to how plants and humans fend off diseases and how invaders stifle immunity.

Microbiologist James Alfano and co-authors reported their findings in Nature, the international weekly journal of science. Their paper was published online April 22 ahead of print publication. The work stems from Alfano's discovery of a protein toxin in a plant pathogen that's also found in several animal pathogens, including those that cause diphtheria and cholera.

"It gives us a whole new avenue to pursue in understanding plant innate immunity," said Alfano, who works on UNL's Plant Science Initiative team.

As different as they are, plants and animals share some of the same molecular components to defend themselves against outside invaders, Alfano explained.

His research focuses on a method of infection found in animal and plant pathogens called a type III protein secretion system. To infect a plant, pathogens inject up to 30 proteins into plant cells using this system, which resembles a kind of microscopic syringe. Once inside, the toxic mix of proteins acts like a burglar, cutting wires to a home's alarm system, disabling the defense system from calling for reinforcements and allowing the intruders to enter unimpeded.

Alfano's team discovered one of the proteins — HopU1 — disrupts the plant's immune system when the disease-causing bacterium Pseudomonas syringae injects it into a plant. This disruption helps the pathogen infect its plant host. Researchers found that HopU1 is a type of enzymatic protein— an ADP-ribosyltransferase that had never before been found in plant pathogens. This type of protein is also found in organisms that cause human diseases such as cholera and diphtheria.

After identifying HopU1 as one of the injected proteins, Alfano began studying which plant components this virulence protein targets. That's key to identifying new components of plant immunity.

The Nature paper reports on the team's discovery that HopU1 modifies RNA-binding proteins. Alfano's work suggests that the pathogen disrupts plant immunity by suppressing immunity-related RNA metabolism — part of the process that turns a plant's DNA code into proteins to help fight off infection. A plant lacking one of the HopU1 targets is more susceptible to the pathogen. These RNA-binding proteins, also found in animals, were not previously known to be part of plants' or animals' immune systems.

Alfano uses Arabidopsis, a well-studied plant, as a model for this research, which is funded by the National Institutes of Health. As his research leads to a better understanding of plant immunity, scientists may be able to genetically modify crop plants to better defend themselves against disease. Because plants and animals share some components of immunity, this basic research one day also could lead to improvements in human health, Alfano said.

Paper co-authors are: Zheng Qing Fu, Ming Guo and Byeong-ryool Jeong, Plant Science Initiative and Department of Plant Pathology; Fang Tian, Plant Science Initiative and School of Biological Sciences; Thomas Elthon, Plant Science Initiative and Department of Agronomy and Horticulture; and Ronald Cerny, Department of Chemistry, all from UNL; and Dorothee Staiger, University of Bielefeld, Germany.

LINCOLN, Neb. -- A team of scientists led by University of Nebraska-Lincoln biochemist Vadim Gladyshev has developed a new way to rapidly identify amino acids in proteins that have redox function. The work is published in the current issue of Science magazine. The process developed by Gladyshev and Dmitri Fomenko, a research assistant professor in Gladyshev's laboratory, focuses on cysteines, amino acids found in most proteins. In some proteins, cysteines have no critical function, while in others they play roles such as binding metals, regulating certain protein functions, or targeting proteins to a particular location in cells. In still other proteins, cysteines are key players in redox regulation, which is a basic biological process used by all organisms. The team's work, which used Prairiefire, UNL's renowned supercomputer, developed a simple, accurate way to determine which cysteines are redox active. Following this bioinformatics procedure, the researchers then verified their technique by characterizing a protein involved in arsenic detoxification, one of many proteins the team has found to contain a redox cysteine. Cysteine appears to be unique among other amino acids found in proteins in that it is amenable to this approach, which provides large-scale, highly selective prediction independent of protein type or organism from which the protein is derived. Other members of the team who coauthored the article are David Thomas and Blakely Adair of the Environmental Protection Agency, and Weibing Xing of the University of North Carolina.