Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 22, 2010
Publication Date: March 15, 2011
Citation: Huffaker, A., Dafoe, N.J., Schmelz, E.A. 2011. ZmPep1, an ortholog of Arabidopsis elicitor Peptide 1, regulates maize innate immunity and enhances disease resistance. Plant Physiology. 155(30):1325-1338. Interpretive Summary: Substantial yield losses occur in maize plants attacked by pathogens. Losses can be decreased through cultural practices or the use of chemicals, but plant resistance is the most effective and environmentally friendly control method. However, the mechanisms of maize disease resistance are still poorly understood. Scientists at the USDA-ARS Center for Medical, Agricultural and Veterinary Entomology in Gainesville, Florida have made an important new finding about how maize plants defend themselves from pathogen attack. They have discovered ZmPep1, a small protein that acts as a signal in maize to trigger immune responses that help protect the plant. This protein signal activates production of plant hormones, jasmonic acid (JA) and ethylene (ET). These hormones prompt maize plants to express genes that encode antimicrobial proteins such as chitinases that degrade fungal cell walls. The ZmPep1 signal also induces the plant to synthesize benzoxazinoid phytoalexins, small highly reactive molecules that protect plants against both insect and microbe invaders. Together, the antimicrobial proteins and phytoalexins can cause injury to, or even kill, attacking pathogens. Just as immunizations protect humans from disease, when maize plants were “immunized” by treatment with ZmPep1, the plants were more disease resistant. ZmPep1 was able to protect both leaves and stems of plants from damage caused by two different fungal diseases; Southern leaf blight and anthracnose stalk rot. This research represents a new understanding of how maize plants protect themselves from microbial attack, and provides a potential method to improve disease resistance in the field.
Technical Abstract: ZmPep1 is a bioactive peptide encoded by a previously uncharacterized maize gene termed ZmPROPEP1. The gene was identified by sequence similarity as an ortholog of the Arabidopsis 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. Potential 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 was unknown. We demonstrate that in maize, the ZmPep1 peptide activates de novo synthesis of the defense-related hormones jasmonic acid (JA) and Ethylene (ET) and induces expression of genes encoding pathogen defense proteins such as Endochitinase A, PR-4, PR protein and the SerPIN proteinase inhibitor. ZmPep1 also stimulates expression of BX1, a gene required for biosynthesis of benzoxazinoid phytoalexins, and accumulation of the benzoxazinoid HDMBOA-Glc in leaves. Peptide-induced accumulation of hormones, defense gene transcripts and HDMBOA-Glc were all found to be dose-dependent, and were elicited in both excised leaves and intact plants. To ascertain whether ZmPep1-induced defenses affect resistance, maize plants were pretreated with the peptide prior to infection with fungal pathogens. As evaluated through measurements of pathogen-induced 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 the elicitor peptide (Pep) family has a conserved function across plant species as endogenous regulators of innate immunity and likely have potential agronomic use to enhance disease resistance in a variety of crops.