Abstract
BackgroundErwinia amylovora is a phytopathogenic bacterium and causal agent of fire blight disease in apples and pears. Although many virulence factors have been characterized, the coordination of expression of these virulence factors in E. amylovora is still not clear. Regulatory small RNAs (sRNAs) are important post-transcriptional regulatory components in bacteria. A large number of sRNAs require the RNA chaperone Hfq for both stability and functional activation. In E. amylovora, Hfq was identified as a major regulator of virulence and various virulence traits. However, information is still lacking about Hfq-dependent sRNAs on a genome scale, including the virulence regulatory functions of these sRNAs in E. amylovora.ResultsUsing both an RNA-seq analysis and a Rho-independent terminator search, 40 candidate Hfq-dependent sRNAs were identified in E. amylovora. The expression and sizes of 12 sRNAs and the sequence boundaries of seven sRNAs were confirmed by Northern blot and 5’ RACE assay respectively. Sequence conservation analysis identified sRNAs conserved only in the Erwinia genus as well as E. amylovora species-specific sRNAs. In addition, a dynamic re-patterning of expression of Hfq-dependent sRNAs was observed at 6 and 12 hours after induction in Hrp-inducing minimal medium. Furthermore, sRNAs that control virulence traits were characterized, among which ArcZ positively controls the type III secretion system (T3SS), amylovoran exopolysaccahride production, biofilm formation, and motility, and negatively modulates attachment while RmaA (Hrs6) and OmrAB both negatively regulate amylovoran production and positively regulate motility.ConclusionsThis study has significantly enhanced our understanding of the Hfq-dependent sRNAs in E. amylovora at the genome level. The identification of multiple virulence-regulating sRNAs also suggests that post-transcriptional regulation by sRNAs may play a role in the deployment of virulence factors needed during varying stages of pathogenesis during host invasion by E. amylovora.Electronic supplementary materialThe online version of this article (doi: 10.1186/1471-2164-15-414) contains supplementary material, which is available to authorized users.
Highlights
Erwinia amylovora is a phytopathogenic bacterium and causal agent of fire blight disease in apples and pears
Hrs6 is a novel Hfq-dependent small RNAs (sRNAs) that was identified for the first time, and we demonstrated that Hrs6 inversely controls amylovoran production and motility in E. amylovora
ArcZ was identified as a virulence-regulating sRNA in our previous study [39], and we found in this study that ArcZ confers pleiotropic regulation on multiple virulence determinants including motility, amylovoran production, attachment, biofilm formation, and the type III secretion system
Summary
Erwinia amylovora is a phytopathogenic bacterium and causal agent of fire blight disease in apples and pears. A large number of sRNAs require the RNA chaperone Hfq for both stability and functional activation. Information is still lacking about Hfq-dependent sRNAs on a genome scale, including the virulence regulatory functions of these sRNAs in E. amylovora. Erwinia amylovora is a phytopathogenic enteric bacterium that causes fire blight, a devastating disease of rosaceous species such as apples and pears. To successfully establish an infection, E. amylovora utilizes a complex regulatory network to sense the relevant environmental signals and coordinate the expression of early and late stage virulence factors involving two component signal transduction systems, bis-(3′-5′)-cyclic diGMP (c-di-GMP), and quorum sensing [2,3,4,5,6,7,8,9,10,11]. The Hfqdependent sRNAs are bound by Hfq, which stabilizes the sRNAs from degradation, and facilitates the interaction of the sRNAs to the target mRNAs [15]
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