retS (PP_4824) encodes a membrane-anchored hybrid sensor histidine kinase of the RetS/Gac signaling family. Domain architecture and orthology support phosphorelay sensor kinase activity, with an N-terminal 7TMR-DISM sensory region, a C-terminal histidine kinase module, and two receiver domains. In Pseudomonas putida KT2440, the direct gene-specific evidence currently supports an upstream negative regulatory role for RetS in K1 type VI secretion system expression during exponential growth. By contrast, the current hyperosmotic-response GO annotation appears to be a family-level transfer without direct KT2440 support.
Definition: Any process that stops, prevents, or reduces the frequency, rate, or extent of protein secretion by the type VI secretion system.
Justification: GO currently provides GO:0033103 for type VI secretion itself and generic regulation-of-secretion terms, but lacks a type VI-specific negative regulation term. RetS-family regulators in Pseudomonas are experimentally shown to repress T6SS expression and activity, and a dedicated term would allow more precise annotation than a generic secretion-regulation parent or repeated use of qualifier-only workarounds.
Parent term: negative regulation of protein secretion
Supporting Evidence:
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000155 phosphorelay sensor kinase activity | IEA GO_REF:0000002 | ACCEPT | Summary: This is the best-supported core molecular function for retS. KEGG assigns PP_4824 to the RetS ortholog group, and UniProt domain architecture matches a membrane hybrid sensor kinase with a histidine kinase catalytic module and receiver domains. Supporting Evidence: file:PSEPK/retS/retS-notes.md PP_4824 is a RetS-family hybrid sensor kinase with 7TMR-DISM, HisKA, and two receiver domains. file:PSEPK/retS/retS-deep-research-falcon.md **cytosolic histidine kinase (HisKA-type) region** plus **tandem receiver (REC/RR) domains** |
| GO:0000160 phosphorelay signal transduction system | IEA GO_REF:0000002 | ACCEPT | Summary: Accept as the core biological-process-level description. RetS is a hybrid two-component sensor kinase, and the KT2440 literature places it upstream in the Gac/RetS signaling network that controls K1-T6SS gene expression. Supporting Evidence: file:PSEPK/retS/retS-notes.md Direct KT2440 evidence supports an upstream signaling role for RetS in the Gac/RetS circuit. file:PSEPK/retS/retS-deep-research-falcon.md RetS is described as an “orphan” or “hybrid” sensor kinase that modulates the GacS/GacA pathway in *Pseudomonas*, often functioning as an upstream antagonist of the Gac/Rsm cascade. |
| GO:0004673 protein histidine kinase activity | IEA GO_REF:0000120 | ACCEPT | Summary: This is a sound enzymatic description of the kinase chemistry carried by RetS. It is slightly less informative than GO:0000155 for this gene because it omits the sensor/phosphorelay context, but it is still correct. Supporting Evidence: UniProt:Q88DK1 RecName: Full=histidine kinase file:PSEPK/retS/retS-deep-research-falcon.md **cytosolic histidine kinase (HisKA-type) region** plus **tandem receiver (REC/RR) domains** |
| GO:0007165 signal transduction | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: This annotation is correct but too broad to represent the core biology of retS on its own. The more informative phosphorelay-specific term GO:0000160 should carry the main process summary. Reason: Correct but generic. The phosphorelay-specific term GO:0000160 better captures the core signaling mechanism, so this broad parent is retained only as non-core context. Supporting Evidence: file:PSEPK/retS/retS-notes.md RetS acts upstream in the Gac/RetS signaling network. file:PSEPK/retS/retS-deep-research-falcon.md RetS-family proteins are described as **inner-membrane sensor kinases** with **periplasmic sensory modules** and **cytoplasmic kinase/receiver modules** |
| GO:0016772 transferase activity, transferring phosphorus-containing groups | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: This is a very high-level parent term of the kinase annotations already present. It adds little beyond GO:0004673 and GO:0000155. Reason: The specific kinase activities already capture the meaningful molecular function. Retaining this broad parent term would reduce interpretability without adding biological precision. |
| GO:0071474 cellular hyperosmotic response | IEA GO_REF:0000118 | UNDECIDED | Summary: Unresolved. The ligand sensed by RetS's periplasmic 7TMR-DISM module is unknown, so an osmotic input can be neither demonstrated nor excluded. The KT2440-specific evidence that exists (repression of K1-T6SS transcription) concerns an output of the pathway and does not speak against an additional osmotic input. Needs an osmotic-shock phenotype or signal-binding assay on PP_4824. Reason: Re-review: changed from REMOVE to UNDECIDED. The rejection rested on the absence of KT2440-specific osmotic evidence rather than on positive contrary evidence, which is not sufficient grounds for removing a phylogenetic inference. Decisively, the falcon deep research states that the ligand sensed by the periplasmic 7TMR-DISM module of RetS is unknown, so an osmotic input can be neither demonstrated nor excluded; a hybrid sensor kinase with an uncharacterised input domain is exactly the case where the sensed stimulus cannot be adjudicated from sequence. The KT2440-specific evidence that does exist (repression of K1-T6SS transcription) concerns an output of the pathway and does not speak against an additional osmotic input. Resolving this needs an osmotic-shock phenotype or signal-binding assay on PP_4824. Supporting Evidence: file:PSEPK/retS/retS-notes.md No direct KT2440 evidence for osmotic-stress signaling by PP_4824 surfaced in the literature reviewed here. file:PSEPK/retS/retS-notes.md The current GO hyperosmotic-response annotation appears to be a family-transfer inference rather than a KT2440-specific experimental result file:PSEPK/retS/retS-deep-research-falcon.md The strongest KT2440-specific experimental evidence currently available from the retrieved literature is that **RetS represses transcription of the K1 type VI secretion system file:PSEPK/retS/retS-deep-research-falcon.md KT2440-specific **signal/ligand identity** for the periplasmic 7TMR‑DISM modules remains unknown |
| GO:0033103 protein secretion by the type VI secretion system | IMP PMID:36748579 Transcriptional organization and regulation of the Pseudomon... | NEW | Summary: Add this as a new process annotation with an upstream negative-effect qualifier. In KT2440, retS mutants derepress K1-T6SS genes during exponential growth, indicating that RetS normally acts upstream to repress this secretion program. Reason: This is the most specific experimentally supported process currently available in GO for the KT2440 phenotype. Because GO lacks a dedicated type VI secretion negative-regulation term, the upstream negative-effect qualifier is the best fit. Falcon deep research corroborates that K1-T6SS is positively regulated by GacS-GacA and repressed by RetS, which inhibits this two-component system. Supporting Evidence: PMID:36748579 The three genes were significantly upregulated in the retS mutant, with fold-changes >3 for hcp1 and >1.5 for tssB1 and PP3104 file:PSEPK/retS/retS-deep-research-falcon.md PP_4824 functions primarily as an **upstream negative regulator of K1‑T6SS transcription**, acting most strongly under conditions where KT2440 would otherwise allocate resources to growth file:PSEPK/retS/retS-deep-research-falcon.md K1‑T6SS expression is **positively regulated by GacS–GacA** and **repressed by RetS**, which inhibits this TCS |
| GO:0005886 plasma membrane | ISS UniProt:Q88DK1 | NEW | Summary: Add the plasma (inner) membrane location. UniProt records a Membrane keyword and five transmembrane helices, and RetS-family proteins are inner-membrane sensor kinases with a periplasmic sensory module and cytoplasmic kinase/receiver modules. This localization is inferred from sequence topology and strong RetS-family conservation rather than direct KT2440 imaging. Reason: The membrane location underpins the sensor role and is used in the core function block; adding it as a NEW CC annotation makes that localization explicit. It is based on UniProt topology (Membrane keyword, TRANSMEM helices) and homology to characterized inner-membrane RetS kinases, so ISS is the appropriate evidence basis. Supporting Evidence: UniProt:Q88DK1 [923 aa membrane histidine kinase with] DOMAIN 404..624 Histidine kinase [...] DOMAIN 642..764 Response regulatory [...] DOMAIN 791..910 Response regulatory [, i.e. a HisKA kinase module plus two receiver domains, with multiple TRANSMEM helices.] file:PSEPK/retS/retS-deep-research-falcon.md RetS-family proteins are described as **inner-membrane sensor kinases** with **periplasmic sensory modules** and **cytoplasmic kinase/receiver modules** file:PSEPK/retS/retS-deep-research-falcon.md PP_4824 senses signals in the periplasm/extracytoplasmic space and transduces them to cytosolic signaling domains |
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Download this section (compressed HTML)Q: What environmental or host-associated ligand is sensed by the N-terminal 7TMR-DISM region of KT2440 RetS?
Suggested experts: Two-component signaling specialists, Pseudomonas sensory physiology researchers
Q: Does KT2440 RetS regulate GacS through direct phosphotransfer or phosphatase interactions, as described for aeruginosa RetS-family systems?
Suggested experts: Signal transduction biochemists, Pseudomonas regulatory network researchers
Q: Beyond K1-T6SS, which KT2440 biofilm or interbacterial competition programs are directly controlled by RetS?
Suggested experts: Rhizosphere ecology researchers, Pseudomonas competition and biofilm groups
Experiment: Construct clean retS deletion, kinase-dead, and receiver-domain phosphosite mutants and quantify K1-T6SS promoter activity, transcript abundance, and Hcp secretion across growth phases.
Hypothesis: RetS represses K1-T6SS transcription during exponential growth through its kinase/phosphorelay module.
Type: Genetics and reporter assays
Experiment: Test direct RetS-GacS interaction, autophosphorylation, phosphotransfer, and phosphatase activity using purified proteins and phosphosite mutants.
Hypothesis: RetS directly modulates the GacS/GacA phosphorelay in KT2440.
Type: Biochemical signaling analysis
Experiment: Screen osmotic, plant-derived, and nutrient cues with RetS reporter strains and purified periplasmic/sensor-domain constructs to identify signals that alter RetS-dependent output.
Hypothesis: The 7TMR-DISM sensory region detects an extracellular cue that links environmental conditions to T6SS repression.
Type: Sensory input mapping
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