Abstract
ZmPep1 is a bioactive peptide encoded by a previously uncharacterized maize (Zea mays) gene, ZmPROPEP1. ZmPROPEP1 was identified by sequence similarity as an ortholog of the Arabidopsis (Arabidopsis thaliana) AtPROPEP1 gene, which encodes the precursor protein of elicitor peptide 1 (AtPep1). Together with its receptors, AtPEPR1 and AtPEPR2, AtPep1 functions to activate and amplify innate immune responses in Arabidopsis and enhances resistance to both Pythium irregulare and Pseudomonas syringae. Candidate orthologs to the AtPROPEP1 gene have been identified from a variety of crop species; however, prior to this study, activities of the respective peptides encoded by these orthologs were unknown. Expression of the ZmPROPEP1 gene is induced by fungal infection and treatment with jasmonic acid or ZmPep1. ZmPep1 activates de novo synthesis of the hormones jasmonic acid and ethylene and induces the expression of genes encoding the defense proteins endochitinase A, PR-4, PRms, and SerPIN. ZmPep1 also stimulates the expression of Benzoxazineless1, a gene required for the biosynthesis of benzoxazinoid defenses, and the accumulation of 2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one glucoside in leaves. To ascertain whether ZmPep1-induced defenses affect resistance, maize plants were pretreated with the peptide prior to infection with fungal pathogens. Based on cell death and lesion severity, ZmPep1 pretreatment was found to enhance resistance to both southern leaf blight and anthracnose stalk rot caused by Cochliobolis heterostrophus and Colletotrichum graminicola, respectively. We present evidence that peptides belonging to the Pep family have a conserved function across plant species as endogenous regulators of innate immunity and may have potential for enhancing disease resistance in crops.
Highlights
Peptides regulate diverse processes pertaining to both development and defense in plants (Matsubayashi and Sakagami, 2006)
Microbe-associated molecular patterns (MAMPs) are molecular fragments recognized by plants as indicators of potential invasion, and peptide MAMPs derived from microbial proteins, such as flg22, elf18 and Pep13, are bound by specific plant pattern-recognition receptors to elicit a cascade of downstream defense responses (Hahlbrock et al, 1995; Zipfel et al, 2004; Zipfel et al, 2006)
We demonstrate that ZmPep1 acts as a defense-regulating signal and extend characterization of this family of peptides beyond Arabidopsis
Summary
Peptides regulate diverse processes pertaining to both development and defense in plants (Matsubayashi and Sakagami, 2006). Peptides can act as molecular messengers during plant interactions with other organisms, alerting the plant to potential attack and inducing defenses. Systemin and hydroxyproline-systemin (HypSys) peptides function as endogenous regulators of defense against herbivores (Ryan and Pearce, 2003; Narváez-Vásquez et al, 2007). Signaling by these peptides promotes a myriad of anti-herbivore responses including accumulation of proteinase inhibitor proteins and of other antinutritive proteins such as polyphenol oxidase, threonine deaminase and arginase as well as systemic emission of volatiles (Pearce et al, 1991; Howe and Jander, 2008; Degenhardt et al, 2010). In Arabidopsis, elicitor peptide 1 (AtPep1) belongs to a family of peptides that interact with the PEPR receptors to regulate expression of pathogen defense genes, including those encoding the PDF1.2 defensin and PR-1 (Huffaker et al, 2006; Yamaguchi et al, 2006; Yamaguchi et al, 2010)
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