Fleites, L. | bioRxiv Science

bioRxiv2026

Antimicrobial peptides expressed by plant-engineered 'symbiont' technology reduces titers and disease symptoms of "Candidatus Liberibacter solanacearum" in potato

Delivery of therapeutic biomolecules into plant vascular tissues remains a challenge in management of vector-borne plant pathogens. The symbiont concept uses reprogrammed Agrobacterium tumefaciens galls (called symbionts) to produce biomolecules while remaining connected to host vasculature. We evaluated whether symbionts expressing antimicrobial peptides (AMPs) suppress Candidatus Liberibacter solanacearum (CLso), the causal agent of potato zebra chip disease. Symbionts were engineered to express a Streptococcus mutans bacteriocin associated with bacterial membrane disruption (Blp-Sm), or an AMP isolated from finger lime and associated with resistance to citrus greening disease (MaSAMP). Effects of AMP-producing symbionts on CLso titers, infection incidence, pathogen movement, and disease symptoms were evaluated in tomato and potato. In tomato, neither AMP significantly reduced CLso titers or infection incidence. However, in potato, AMP-producing symbionts reduced CLso accumulation and movement from CLso-inoculated source shoots into non-inoculated sink shoots connected through underground tubers. Blp-Sm produced the strongest reduction in CLso accumulation and infection incidence in sink tissues. In separate assays where symbionts were established directly on potato seed tubers, MaSAMP significantly reduced CLso titers in stems and tubers and reduced zebra chip symptoms in tubers, despite no reduction of CLso titers in terminal leaves. These findings demonstrate that AMP-producing symbionts suppress vascular pathogen accumulation and movement within plants and highlight the symbiont concept as a potential platform for managing diseases caused by vascular-restricted pathogens. Further, they show the potato-CLso system is a promising infection model to both refine and improve symbiont technology, and to test additional AMPs for potency against related pathogens.

plant biology↗

bioRxiv2023

Plant-derived, nodule-specific cysteine rich peptides inhibit growth and psyllid acquisition of 'Candidatus Liberibacter asiaticus', the citrus Huanglongbing bacterium

AbstractThe 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 to prevent the spread of the disease into new citrus growing regions. However, identifying control strategies to block HLB transmission poses significant challenges, such as the discovery and delivery of antimicrobial compounds targeting the bacterium and overcoming consumer hesitancy towards accepting the treatment. Here, we computationally identified and tested a series of 20-mer nodule-specific cysteine-rich peptides (NCRs) derived from the Mediterranean legume, Medicago truncatula Gaertn. (barrelclover) to identify those peptides that could effectively prevent or reduce CLas infection in citrus leaves and/or prevent CLas acquisition by the bacteriums insect vector, D. citri. A set of NCR peptides were tested in a screening pipeline involving three distinct assays: a bacterial culture assay, a CLas-infected excised citrus leaf assay, and a CLas-infected nymph acquisition assay that included D. citri nymphs, the only stage of D. citris life-cycle that can acquire CLas leading to the development of vector competent adult insects. We demonstrate that a subset of M. truncatula-derived NCRs inhibit both CLas growth in citrus leaves and CLas acquisition by D. citri from CLas-infected leaves. These findings reveal NCR peptides as a new class and source of biopesticide molecules to control CLas for the prevention and/or treatment of HLB.

plant biology↗