Identification of plant-derived nodule-specific cysteine rich peptides that are antimicrobial against “Candidatus Liberibacter asiaticus”, the citrus greening disease bacterium

Authors: HIGGINS, STEVEN - Former ARS Employee; IGWE, DAVID - Cornell University; Coradetti, Samuel; Ramsey, John; Deblasio, Stacy; PITINO, MARCO - Agrosource, Inc; Niedz, Randall; Shatters, Robert; Fleites, Laura; Heck, Michelle

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2024
Publication Date: 5/30/2024
Citation: Higgins, S.A., Igwe, D.O., Coradetti, S., Ramsey, J.S., Deblasio, S.L., Pitino, M., Niedz, R.P., Shatters, R.G., Fleites, L.A., Heck, M.L. 2024. Identification of plant-derived nodule-specific cysteine rich peptides that are antimicrobial against “Candidatus Liberibacter asiaticus”, the citrus greening disease bacterium. Phytopathology. 114:971-981. https://doi.org/10.1094/PHYTO-09-23-0322-KC.
DOI: https://doi.org/10.1094/PHYTO-09-23-0322-KC

Interpretive Summary: Citrus growers need effective strategies for managing citrus greening disease, also known as Huanglongbing (HLB). The presence and, therefore, the likely spread, of HLB within California are a major concern for growers because of the mobility of the Asian citrus psyllid (ACP), the insect vector of citrus greening in the United States. In Florida, the disease is endemic and growers need treatments to mitigate infection in existing groves and prevent transmission into new plantings. Organic growers, in particular, seek HLB management strategies that do not rely on synthetic chemicals. This research paper describes the discovery of plant-derived peptides that have the ability to thwart the acquisition of the HLB bacterium by the ACP. These peptides have different killing modes of action that could effectively control citrus greening and/or prevent ACP from transmitting the pathogen to citrus trees.

Technical Abstract: The Asian citrus psyllid, Diaphorina citri, is a vector of ‘Candidatus Liberibacter asiaticus’ (CLas), a gram-negative, obligate biotroph whose infection in Citrus species is associated with citrus greening disease, or Huanglongbing (HLB). Strategies to block CLas transmission by D. citri remain the best way at preventing the spread of the disease into new citrus growing regions. HLB control strategies pose hefty challenges, both on the consumer acceptance side and on the discovery and delivery of antimicrobial compounds that target the bacterium. Here, we computationally identified and tested a series of 20-mer nodule-specific cysteine-rich peptides (NCRs) derived from the Mediterranean legume, Medicago truncatula (barrelclover) to identify those peptides that could effectively prevent or reduce CLas infection in citrus leaves and/or prevent CLas acquisition by the insect vector. A set of NCR peptides were tested in a screening pipeline involving three distinct assays: to test in three distinct assays: a bacterial culture assay, a CLas-infected excised citrus leaf assay and a CLas-infected excised leaf acquisition assay that included D. citri nymphs, which are the only stage of the vector’s life-cycle that can acquire CLas leading to the development of vector competent adults. We demonstrate that a subset of M. truncatula-derived NCRs inhibit CLas growth in citrus leaves and/or reduce acquisition from CLas-infected leaves by D. citri. These findings confirm NCR peptides as a new class and source of biopesticide molecules that could be used to control CLas for the prevention or treatment of HLB.