AUTHOR=Aguilera-Herce Julia , Zarkani Azhar A. , Schikora Adam , Ramos-Morales Francisco 

TITLE=Dual Expression of the Salmonella Effector SrfJ in Mammalian Cells and Plants

JOURNAL=Frontiers in Microbiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2017.02410

DOI=10.3389/fmicb.2017.02410

ISSN=1664-302X

ABSTRACT=<p>SrfJ is an effector of the <italic>Salmonella</italic> pathogenicity island 2-encoded type III secretion system. <italic>Salmonella enterica</italic> serovar Typhimurium expresses <italic>srfJ</italic> under two disparate sets of conditions: media with low Mg<sup>2+</sup> and low pH, imitating intravacuolar conditions, and media with <italic>myo</italic>-inositol (MI), a carbohydrate that can be used by <italic>Salmonella</italic> as sole carbon source. We investigated the molecular basis for this dual regulation. Here, we provide evidence for the existence of two distinct promoters that control the expression of <italic>srfJ</italic>. A proximal promoter, P<italic>srfJ</italic>, responds to intravacuolar signals and is positively regulated by SsrB and PhoP and negatively regulated by RcsB. A second distant promoter, P<italic>iolE</italic>, is negatively regulated by the MI island repressor IolR. We also explored the <italic>in vivo</italic> activity of these promoters in different hosts. Interestingly, our results indicate that the proximal promoter is specifically active inside mammalian cells whereas the distant one is expressed upon <italic>Salmonella</italic> colonization of plants. Importantly, we also found that inappropriate expression of <italic>srfJ</italic> leads to reduced proliferation inside macrophages whereas lack of <italic>srfJ</italic> expression increases survival and decreases activation of defense responses in plants. These observations suggest that SrfJ is a relevant factor in the interplay between <italic>Salmonella</italic> and hosts of different kingdoms.</p>