Physiological and Transcriptional Responses to Osmotic Stress of Two Pseudomonas syringae Strains That Differ in Epiphytic Fitness and Osmotolerance

Freeman, Brian C.; Chen, Chyi‐Liang; Yu, Xilan; Nielsen, Lindsey; Peterson, Kelly; Beattie, Gwyn A.

doi:10.1128/jb.00787-13

Cited by 57 publications

(58 citation statements)

References 61 publications

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“…For example, only one P. syringae pv. tomato DC3000 gene (1/12 genes) that functions in alginate production was induced by salt stress (22); in contrast, all of these were strongly induced by AlgU in the present study (see Table S1 in the supplemental material). In this case, the one saltinduced alginate biosynthesis gene (algC) is influenced by AlgR, a response regulator, which is activated by salt stress in other pseudomonads (72).…”

Section: Discussioncontrasting

confidence: 44%

“…syringae B728a cells exposed to osmotic stress (21). However, based on data presented here and published data (22), osmotic stress exposure affects P. syringae pv. syringae B728a and P. syringae pv.…”

Section: Discussioncontrasting

confidence: 40%

“…Nearly all of these important pathogenesis genes (23/24) were regulated differently in comparison of AlgU-and salt-dependent gene expression in P. syringae pv. tomato DC3000, including 9 genes that were induced by AlgU but repressed in osmotic stress (22). But, as with many biological systems, the genes controlled by these processes are not entirely mutually exclusive.…”

Section: Discussionmentioning

confidence: 99%

“…This study also found that AlgU-dependent transcription was induced in response to osmotic stress (21), and there is a great deal of overlapping regulation between the osmotic stress stimulon and the algU regulon in P. syringae pv. syringae B728a, suggesting that osmolarity is a key signal for AlgU activation in this pathovar (21,22). But, the role of AlgU may be different in P. syringae pv.…”

mentioning

confidence: 94%

“…But, the role of AlgU may be different in P. syringae pv. tomato DC3000 since key indicators of AlgU regulation (i.e., expression of alginate biosynthesis genes) were not induced by osmotic stress (22). These differences in AlgU-dependent regulation and sensing are likely indicative of the different strategies for environmental adaptation and plant association used by these pathovars.…”

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confidence: 99%

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AlgU Controls Expression of Virulence Genes in Pseudomonas syringae pv. tomato DC3000

et al. 2016

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Plant-pathogenic bacteria are able to integrate information about their environment and adjust gene expression to provide adaptive functions. AlgU, an extracytoplasmic function (ECF) sigma factor encoded by Pseudomonas syringae, controls expression of genes for alginate biosynthesis and genes involved with resisting osmotic and oxidative stress. AlgU is active while these bacteria are associated with plants, where its presence supports bacterial growth and disease symptoms. We found that AlgU is an important virulence factor for P. syringae pv. tomato DC3000 but that alginate production is dispensable for disease in host plants. This implies that AlgU regulates additional genes that facilitate bacterial pathogenesis. We used transcriptome sequencing (RNA-seq) to characterize the AlgU regulon and chromatin immunoprecipitation sequencing (ChIP-seq) to identify AlgUregulated promoters associated with genes directly controlled by this sigma factor. We found that in addition to genes involved with alginate and osmotic and oxidative stress responses, AlgU regulates genes with known virulence functions, including components of the Hrp type III secretion system, virulence effectors, and the hrpL and hrpRS transcription regulators. These data suggest that P. syringae pv. tomato DC3000 has adapted to use signals that activate AlgU to induce expression of important virulence functions that facilitate survival and disease in plants. IMPORTANCEPlant immune systems produce antimicrobial and bacteriostatic conditions in response to bacterial infection. Plant-pathogenic bacteria are adapted to suppress and/or tolerate these conditions; however, the mechanisms controlling these bacterial systems are largely uncharacterized. The work presented here provides a mechanistic explanation for how P. syringae pv. tomato DC3000 coordinates expression of multiple genetic systems, including those dedicated to pathogenicity, in response to environmental conditions. This work demonstrates the scope of AlgU regulation in P. syringae pv. tomato DC3000 and characterizes the promoter sequence regulated by AlgU in these bacteria. Pseudomonas syringae is a globally dispersed plant-pathogenic bacterium adapted to live in many diverse environments, which in some cases expose bacteria to stresses that can interfere with their growth and survival. Counteracting or tolerating these stresses requires coordinated expression of specific physiologic traits. These responses are controlled by environmental sensing and signal transduction systems that detect information about external conditions and induce changes in transcription. The extracytoplasmic function (ECF) sigma factors are one type of system providing this function in bacteria and are capable of inducing sets of genes (regulons) in response to environmental stimuli (1). ECF sigma factor activity is often controlled by a cytoplasmic membrane-bound anti-sigma factor that forms a complex with the ECF sigma factor (2). Under inducing conditions, the ECF sigma factor is liberated from the anti-...

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Section: Discussioncontrasting

confidence: 44%

Section: Discussioncontrasting

confidence: 40%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 94%

mentioning

confidence: 99%

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