Lso-HPE1, an effector of 'Candidatus Liberibacter solanacearum' can repress plant immune response.

'Candidatus Liberibacter solanacearum' (Lso) is a plant pathogen affecting Solanaceae and Apiaceae in different parts of the world. 'Candidatus Liberibacter 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 and/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 Lso protein, Lso-HPE1 (hypothetical protein effector1). We compared this protein sequence in the different Lso haplotypes. We predicted the signal peptide and validated its function using Escherichia coli's alkaline phosphatase fusion assay. Agrobacterium tumefaciens-mediated transient expression in Nicotiana benthamiana demonstrated that Lso-HPE1 from Lso 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 Lso haplotypes A and B in tomato and in the vector, Bactericera cockerelli. This work validates the identification of a Sec-translocon dependent Lso protein possibly involved in suppression of plant cell death.