Plant-derived, nodule-specific cysteine rich peptides inhibit growth and psyllid acquisition of ‘CandidatusLiberibacter asiaticus’, the citrus Huanglongbing bacterium

Abstract

AbstractThe Asian citrus psyllid,Diaphorina citri, is a vector of ‘CandidatusLiberibacter asiaticus’ (CLas), a gram-negative, obligate biotroph whose infection inCitrusspecies is associated with citrus greening disease, or Huanglongbing (HLB). Strategies to blockCLas transmission byD. citriremain 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 truncatulaGaertn. (barrelclover) to identify those peptides that could effectively prevent or reduceCLas infection in citrus leaves and/or preventCLas acquisition by the bacterium’s insect vector,D. citri. A set of NCR peptides were tested in a screening pipeline involving three distinct assays: a bacterial culture assay, aCLas-infected excised citrus leaf assay, and aCLas-infected nymph acquisition assay that includedD. citrinymphs, the only stage ofD. citri’s life-cycle that can acquireCLas leading to the development of vector competent adult insects. We demonstrate that a subset ofM. truncatula-derived NCRs inhibit bothCLas growth in citrus leaves andCLas acquisition byD. citrifromCLas-infected leaves. These findings reveal NCR peptides as a new class and source of biopesticide molecules to controlCLas for the prevention and/or treatment of HLB.