| AtPep1 is a 23 amino acid peptide that was isolated from Arabidopsis thaliana in a screen for bioactive peptides with the ability to inhibit proton efflux in suspension-cultured cells (G. Pearce, A. Huffaker, C. A. Ryan, submitted). Upon isolation, no physiological role in planta was known for AtPep1. The peptide is derived from a larger precursor protein (proAtPep1), as found with many peptide hormones in animals and plants. Wounding or exposing plants to the volatile defense hormone methyl jasmonate (MeJA) induced expression of the gene encoding proAtPep1. Supplying Arabidopsis plants with the AtPep1 peptide through cut stems also induced proAtPep1 gene expression as well as expression of genes encoding plant defensin (PDF1.2) and pathogenesis-related protein 1 (PR-1), two defense proteins of Arabidopsis . To investigate whether AtPep1 is involved in defense, the proAtPep1 gene was constitutively overexpressed in Arabidopsis. Expression of genes encoding the defense proteins PDF1.2, PR-1 and tyrosine amino transferase (TAT) was upregulated in the transgenic plants. When these plants were challenged with the oomycete root pathogen Pythium irregulare, they exhibited increased resistance compared to wild-type plants, evidenced by a more robust leaf and root growth upon infection. These results indicate that AtPep1 may be a novel peptide signal that is a component of the jasmonate-based signal transduction pathway regulating plant defense against pathogens. ProAtPep1 belongs to a small gene family in Arabidopsis with tissue-specific paralogs that exhibit constitutive and MeJA-inducible expression. Orthologs of the proAtPep1 gene have been identified in many important crop species including canola, soybean, potato, rice and poplar, and future work could lead to increased resistance against pathogens in these plants as well. |
