Plant-Derived, Nodule-Specific Cysteine-Rich Peptides as a Novel Source of Biopesticides for Controlling Citrus Greening Disease
Steven Higgins, David Okeh Igwe, Samuel T. Coradetti, John S. Ramsey, Stacy L. DeBlasio, Marco Pitino, Robert G. Shatters, Randall P. Niedz, Laura A. Fleites, Michelle Heck
Abstract
Nodule-specific cysteine-rich (NCR) peptides, encoded in the genome of the Mediterranean legume Medicago truncatula (barrelclover), are known to regulate plant−microbe interactions. A subset of computationally derived 20-mer peptide fragments from 182 NCR peptides was synthesized to identify those with activity against the unculturable vascular pathogen associated with citrus greening disease, ‘ Candidatus Liberibacter asiaticus’ ( CLas). Grounded in a design of experiments framework, we evaluated the peptides in a screening pipeline involving three distinct assays: a bacterial culture assay with Liberibacter crescens, a CLas-infected excised citrus leaf assay, and an assay to evaluate effects on bacterial acquisition by the nymphal stage of hemipteran vector Diaphorina citri. A subset of the 20-mer NCR peptide fragments inhibits both CLas growth in citrus leaves and CLas acquisition by D. citri. Two peptides induced higher levels of D. citri mortality. These findings reveal 20-mer NCR peptides as a new class of plant-derived biopesticide molecules to control citrus greening disease.