Lso-HPE1, an Effector of ‘<i>Candidatus</i> Liberibacter solanacearum’, Can Repress Plant Immune Response

Abstract

'<i>Candidatus</i> Liberibacter solanacearum' is a plant pathogen affecting the families Solanaceae and Apiaceae in different parts of the world. '<i>Ca.</i> L. solanacearum' is a Gram-negative, fastidious α-proteobacterium that is vectored by different psyllid species. Plant-pathogenic bacteria are known for interfering with the host physiology or defense mechanisms, often by secreting bacterial effectors. Effector proteins are critical for virulence; therefore, the identification of effectors could help with disease management. In this study, we characterized the Sec-translocon-dependent '<i>Ca.</i> L. solanacearum'-hypothetical protein effector 1 (Lso-HPE1). We compared this protein sequence in the different '<i>Ca.</i> L. solanacearum' haplotypes. We predicted the signal peptide and validated its function using <i>Escherichia coli</i>'s alkaline phosphatase fusion assay. <i>Agrobacterium tumefaciens</i>-mediated transient expression in <i>Nicotiana benthamiana</i> demonstrated that Lso-HPE1 from '<i>Ca.</i> L. solanacearum' haplotypes A and B were able to inhibit the induction of cell death in plants. We also compared gene expression of the Lso-HPE1- transcripts in '<i>Ca.</i> L. solanacearum' haplotypes A and B in tomato and in the vector <i>Bactericera cockerelli</i>. This work validates the identification of a Sec-translocon-dependent '<i>Ca.</i> L. solanacearum' protein possibly involved in suppression of plant cell death.