A new molecule discovered in the battle between plants and disease

July 19, 2005

Scientists at Washington State University in Pullman have discovered a molecule that plays a role in the battle plants must win against bacteria and fungi that would eat them for lunch. The group led by Professor Clarence A. "Bud" Ryan isolated a small protein called Pep1 that appears to act like a hormone, signaling to the rest of the plant to raise its defenses at the first sign of an infection. They also discovered the receptor protein to which Pep1 binds to exert its protective effects.

Pep1 was isolated from the plant Arabidopsis thaliana, which is a species favored by investigators for attributes that facilitate experimentation, but the same molecule is found in crop species such as canola, soybean, potato, tomato, rice, and poplar. Therefore, further work on Pep1 and its receptor could lead to a general increase in the resistance of crops to pathogens, which could greatly benefit farmers. Already, the researchers have used the Pep1 gene to increase the resistance of Arabidopsis plants to a fungal pathogen called Pythium irregulare.

These findings will be presented July 20, at 11:20 at the ASPB meeting at the Washington State Convention and Trade Center in Seattle, WA.

The abstract, #9183, is below:
Authors:
Presenter: Huffaker, Alisa
Authors: Huffaker, Alisa (A) alisamari@yahoo.com; Pearce, Gregory (A) pearceg@mail.wsu.edu; Ryan, Clarence, A (A) cabudryan@hotmail.com;

Affiliations: (A): Institute of Biological Chemistry, Washington State University

Title: A novel peptide signal, AtPep1, regulates pathogen defense in Arabidopsis

AtPep1 is a 23 amino acid peptide that was isolated from Arabidopsis thaliana (G. Pearce, A. Huffaker, C.A. Ryan, submitted). The peptide is encoded by a gene at the locus At5g64900 and is derived from the carboxyl terminus of a 92 amino acid precursor, proAtPep1, a scenario commonly found in both animal and plant peptide precursors. No physiological role was known for AtPep1, and a function was sought in Arabidopsis by incubating plants under a variety of conditions and monitoring expression of the proAtPep1 gene. Cold and dehydration stress and exposure to ABA or MeSA did not affect the expression of proAtPep1, but wounding, exposing plants to methyl jasmonate (MeJA), or supplying plants with the AtPep1 peptide through cut petioles induced expression of the gene. Also expressed in response to AtPep1 were the PDF1.2 gene (a plant defensin) and the PR-1 gene, (a pathogenesis-related gene). Two wound-related genes, LOX2 and VSP2, were not induced by AtPep1. Supplying AtPep1 to jasmonate-deficient fad3-2 fad7-2 fad8 mutant plants did not induce the proAtPep1, PDF1.2 or PR-1 genes, indicating that AtPep1 signaling involves the octadecanoid pathway. AtPep1 induction of defense genes in excised Arabidopsis leaves was inhibited by DPI, implicating the generation of H2O2 in the signaling pathway. Constitutively overexpressing the proAtPep1 gene in Arabidopsis induced a constitutive activation of PDF1.2, PR-1, and tyrosine amino transferase (TAT3) genes, but not the expression of LOX2 or VSP2 genes. The transgenic plants were more resistant toward the oomycete root pathogen Pythium irregulare than wild-type plants, evidenced by a more robust leaf and root growth upon infection. ProAtPep1 belongs to a seven member gene family in Arabidopsis with tissue-specific paralogs that exhibit differential expression profiles. Orthologs of the proAtPep1 gene have been identified in important crop species including canola, soybean, potato, tomato, rice and poplar.
-end-
Supported in part by the National Science Foundation grant IBN 0090766, and by the Charlotte Y. Martin Foundation.

American Society of Plant Biologists

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