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Analyzing the expression of Candidatus Liberibacter solanacearum effectors in insect and plant hosts

Paola Reyes Caldas: University of California

<div><span class="s1"><i>Candidatus</i> Liberibacter solanacearum (Lso), the causal agent of Zebra Chip disease, is an emerging pathogen causing significant crop losses in Solanaceous plants. There are no commercial cultivars with resistance to Zebra Chip, making disease management difficult. Lso haplotypes A and B are transmitted by the psyllid vector<i> Bactericera cockerelli</i> and infect the phloem of tomato and potato. Many bacterial pathogens secrete effectors to manipulate and establish in their hosts. Genome analyses revealed the presence of the SEC secretion system in Lso. We utilized available genome sequences to predict conserved SEC-dependent effectors from haplotype A (R1, Lso-NZ1, HenneA), haplotype B (CLso-Z1), and haplotype C (FIN111, FIN114). Effectors were predicted according to the presence of the secretory signal peptide using SignalP 3.0 and 4.0, proteins smaller than 25 KDa without a transmembrane domain were selected and manually verified. We identified a suite of core effectors present in haplotypes infecting tomato and potato. The expression of core Lso effectors was analyzed in plant and insect hosts by qPCR, identifying those that are preferentially expressed in either organism. Lso effector expression patterns could be used to predict the role of individual proteins in colonizing the insect vector and plant host. A greater understanding of how phloem-limited bacterial pathogens interact with their hosts can ultimately be used to develop targeted disease control strategies.</span></div>