Characterizing the in vivo role of Scabin, a mono ADP- ribosyltransferase from the common scab pathogen Streptomyces scabiei

Perry, Hannah Claire (2021) Characterizing the in vivo role of Scabin, a mono ADP- ribosyltransferase from the common scab pathogen Streptomyces scabiei. Masters thesis, Memorial University of Newfoundland.

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Abstract

Common scab is a widespread bacterial disease of potato and other root and tuber crops. The disease is characterized by the presence of superficial, raised or deep-pitted lesions on the surface of the potato tuber, and these lesions reduce the market value of the crop to cause major economic losses for farmers. To date, no fully resistant potato cultivar exists, and current management strategies are largely inadequate or inconsistent. Therefore, studying the virulence factors of the most prominent causative agent, Streptomyces scabiei, is of high importance. Recently, a new putative virulence factor called Scabin was identified in the genome of S. scabiei. Scabin is a mono ADP-ribosyltransferase that possesses in vitro activity towards DNA, RNA and small guanosine-containing molecules, a rare activity for this group of enzymes that typically target proteins. However, the in vivo target and role of Scabin remains unknown. The purpose of this study has been to investigate the function of Scabin and determine if it plays a role in S. scabiei pathogenesis. To achieve this, a scabin knockout mutant was created, and the mutant together with wild-type S. scabiei and a scabin overexpression strain were tested in several plant bioassays. The morphology of the mutant and overexpression strain was examined when the strains were cultured on several distinct agar media. The conditions under which scabin is expressed were investigated using RT-PCR, and subsequently, it was discovered that scabin is co-transcribed with a neighbouring gene, SCAB_27781, suggesting they are functionally linked. The distribution of Scabin and SCAB_27781 homologues in other Streptomyces species and the relative positions of the corresponding genes in each species were mapped out, and regions of interest in both proteins were predicted using various bioinformatic tools. This study is the first to investigate possible in vivo roles for Scabin.

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