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ARS Home » Pacific West Area » Parlier, California » San Joaquin Valley Agricultural Sciences Center » Crop Diseases, Pests and Genetics Research » Research » Publications at this Location » Publication #339003
Title: Characterization of the Serralysin-like gene of 'Candidatus Liberibacter solanacearum' associated with Potato Zebra Chip disease

Author
item RAVINDRAN, ARAVIND - Texas A&M University
item SAENKHAM, PANATDA - Texas A&M University
item LEVY, JULIEN - Texas A&M University
item Lin, Hong
item GROSS, DENNIS - Texas A&M University
item PIERSON, ELIZABETH - Texas A&M University

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2017
Publication Date: 11/6/2017
Citation: Ravindran, A., Saenkham, P., Levy, J., Lin, H., Gross, D.C., Pierson, E. 2017. Characterization of the Serralysin-like gene of 'Candidatus Liberibacter solanacearum' associated with Potato Zebra Chip disease. Phytopathology. 108(3):327-335. https://doi.org/10.1094/PHYTO-02-17-0064-R.
DOI: https://doi.org/10.1094/PHYTO-02-17-0064-R

Interpretive Summary: ‘Candidatus Liberibacter solanacearum’ (Lso) is the causative agent of zebra chip (ZC) disease of potato. The disease affects all cultivated varieties, resulting in significant revenue losses to commercial potato growers in the United States. The goal of this study was to determine virulence genes/factors responsible for the disease. Analysis of genome data suggested that Lso serralysin-like protease could be a potent virulence factor. Pathogenicity assay showed that the expression of serralysin-like protease was up regulated in Lso-infected plants while no proteolytic activity was detected in vitro experiments. Identification of Lso virulence determinants will facilitate development of target-based disease management.

Technical Abstract: The non-culturable bacterium ‘Candidatus Liberibacter solanacearum’ (Lso) is the causative agent of zebra chip disease in potato. Computational analysis of the Lso genome revealed a serralysin-like gene based on conserved domains characteristic of genes encoding metalloprotease enzymes similar to serralysin. Serralysin, first described from Serratia, and other serralysin family metalloprotease are secreted by the type I secretion system (T1SS) and typically are characterized as virulence factors. The Lso serralysin-like gene is located next to and divergently transcribed from genes encoding a T1SS. Based on its relationship to the T1SS and the role of other serralysin family proteases in circumventing host antimicrobial defenses, it has been speculated that a functional Lso serralysin-like protease could be a potent Lso virulence factor. The goals of this study were to further describe the Lso serralysin-like gene sequence and predicted protein compared to other serralysin-like genes, to observe expression of this gene in planta, to determine whether the Lso serralysin-like gene encodes a functional protease, and if so, whether it is required for zebra chip disease development. A previously-constructed serralysin-deficient mutant of S. liquefaciens FK01, an endophyte associated with insects, as well as an serralysin mutant strain of E. coli were used as surrogates for expression analysis of the Lso serralysin-like gene. The Lso protein was expressed as both an intact 55 kDa protein and as a chimeric S. liquefaciens-Lso serralysin-like protein to facilitate secretion in the S. liquefaciens surrogate. The Lso protein was also expressed as an intact and a truncated protein containing just the putative catalytic domains in the E. coli surrogate. Pathogenicity assay showed that the expression of serralysin-like protease was up regulated in Lso-infected plants while no proteolytic activity was detected in vitro experiments suggesting additional cofactors or substrate specificity are required for Lso serralysin-like protease activity.