The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
The Pseudomonas putida KT2440 gene fliA encodes FliA (σ28; sigma-28 / sigma-F), an alternative RNA polymerase sigma factor that directs transcription of late (flagellar/chemotaxis) genes in the flagellar regulatory cascade. In KT2440, FliA is positioned downstream of the master regulator FleQ and σ54 (RpoN) and is activated post-translationally by release from the anti-sigma factor FlgM after hook–basal body completion. Evidence in KT2440 further supports a role for FliA in coupling motility to the second messenger c-di-GMP through partial control of bifA, a c-di-GMP phosphodiesterase important for swimming behavior. (leal‐morales2022transcriptionalorganizationand pages 1-1, leal‐morales2022transcriptionalorganizationand pages 14-14, xiao2017expressionofthe pages 5-7)
FliA is an alternative sigma factor that binds core RNA polymerase (RNAP) to alter promoter recognition specificity. In P. putida KT2440, this is explicitly described as FliA “conferr[ing] promoter-recognition specificity to core RNA polymerase (RNAP),” consistent with sigma-factor biology. (xiao2017expressionofthe pages 4-5, xiao2017expressionofthe pages 5-7)
A detailed KT2440 model describes a three-tier transcriptional cascade:
- Class I: fleQ is at the top of the hierarchy. (leal‐morales2022transcriptionalorganizationand pages 1-1)
- Class II: FleQ- and σ54-dependent genes encode most basal body/structural components and regulatory elements including fliA. (leal‐morales2022transcriptionalorganizationand pages 1-1, leal‐morales2022transcriptionalorganizationand media 34a91b68)
- Class III: FliA-dependent transcription enables synthesis of the filament, at least one stator complex, and completion of the chemotaxis apparatus. (leal‐morales2022transcriptionalorganizationand pages 1-1, leal‐morales2022transcriptionalorganizationand media 34a91b68)
Quantitatively, the KT2440 flagellar cluster is reported to contain 59 genes, organized into 11 operons with 22 primary/internal promoters, highlighting extensive transcriptional complexity that FliA participates in at the late tier. (leal‐morales2022transcriptionalorganizationand pages 1-1)
FliA is regulated by the anti-sigma factor FlgM, which sequesters FliA until flagellar assembly reaches a checkpoint. In P. putida, the “final tier” is triggered when FliA is released from inactivation by FlgM, after FlgM secretion via the flagellar type III secretion system (FT3SS) upon hook completion. (leal‐morales2022transcriptionalorganizationand pages 14-14)
A 2024 expert review in Pseudomonas further frames this as a conserved mechanism in which hook–basal body completion enables FlgM export and thus FliA activation. (oladosu2024fliptheswitch pages 3-4)
A 2024 review (focused on P. aeruginosa but widely used as a mechanistic reference for pseudomonads) summarizes:
- FliA (RpoF, σ28) drives Class IV flagellar gene expression once released from FlgM. (oladosu2024fliptheswitch pages 3-4)
- It lists representative FliA-dependent genes such as fliC, motAB, and multiple chemotaxis genes (e.g., cheAB, cheW, cheVR, cheYZ) and flgMN. (oladosu2024fliptheswitch pages 3-4)
Although these named targets are from P. aeruginosa, they align with P. putida KT2440’s late-tier role for FliA in completing filament/chemotaxis/stator function and provide an expert-curated framework for interpreting the conserved FliA module. (leal‐morales2022transcriptionalorganizationand pages 1-1, oladosu2024fliptheswitch pages 3-4)
A 2023 review of P. aeruginosa transcriptional regulators states that σFliA (σ28) controls flagellar biosynthesis genes and is essential for motility, with its activity modulated by FlgM and additional partner-switching layers that interface with global signaling (Rsm-related pathways). (sanchezjimenez2023transcriptionalregulatorscontrolling pages 18-19)
The same review reports transcriptomic evidence in P. aeruginosa that a fliA mutant shows downregulation of multiple secretion-system genes (T2SS/T3SS/T6SS components), suggesting that in some pseudomonads FliA can be a broader node connecting motility and virulence-associated functions. This should be treated as cross-species context rather than KT2440-specific annotation. (sanchezjimenez2023transcriptionalregulatorscontrolling pages 19-21)
In KT2440, FliA’s primary molecular function is to function as an RNAP sigma factor that recognizes σ28-type promoters to activate late flagellar/chemotaxis transcription. (leal‐morales2022transcriptionalorganizationand pages 1-1, xiao2017expressionofthe pages 4-5)
In KT2440 the late output of FliA activity is explicitly described: filament synthesis, activation of at least one stator complex, and completion of the chemotaxis apparatus. (leal‐morales2022transcriptionalorganizationand pages 1-1)
The regulatory logic is consistent with a checkpoint model: completion of the hook triggers secretion of FlgM, which removes inhibition and enables robust transcription of late genes. (leal‐morales2022transcriptionalorganizationand pages 14-14)
Leal-Morales et al. (2022) report systematic promoter motif discovery in the KT2440 flagellar cluster, with 21 putative flagellar promoters and explicit identification of FliA-dependent promoter motifs upstream of fliK2, fliC, and cheV, and additional matches upstream of fliS and flgM. (leal‐morales2022transcriptionalorganizationand pages 6-6)
Promoter-motif alignments and the overall transcriptional cascade schematic are shown in the paper’s figures (promoter motif alignments and tiered cascade). (leal‐morales2022transcriptionalorganizationand media ffe1d522, leal‐morales2022transcriptionalorganizationand media 34a91b68)
A KT2440 targeted mechanistic study demonstrated that bifA (encoding a c-di-GMP phosphodiesterase) is partly controlled by FliA:
- fliA deletion caused an approximately twofold decrease in bifA transcription/promoter activity and produced a nonmotile phenotype that could be complemented by fliA expression. (xiao2017expressionofthe pages 4-5, xiao2017expressionofthe pages 1-2)
- 5′-RACE identified two transcription start sites for bifA (at 103 nt and 40 nt upstream of the start codon), with upstream σ70 and σ28 promoter elements, indicating dual control (basal σ70 and enhancing σ28/FliA). (xiao2017expressionofthe pages 5-7)
- Promoter mutagenesis in the σ28 region reduced activity in wild type but not in a fliA mutant, supporting FliA dependence for that promoter component. (xiao2017expressionofthe pages 5-7)
This establishes an experimentally supported mechanistic bridge between the flagellar sigma factor and second-messenger regulation relevant to motility transitions (swimming vs sessility). (xiao2017expressionofthe pages 5-7, xiao2017expressionofthe pages 8-9)
FliA is not a secreted or membrane-embedded protein; it functions by associating with cytosolic RNAP and acting at chromosomal promoters. KT2440 literature describes FliA as conferring promoter specificity to core RNAP, implying its functional localization is the cytosol/nucleoid region where RNAP-DNA transcription occurs. (xiao2017expressionofthe pages 4-5, xiao2017expressionofthe pages 5-7)
Its activity is conditioned by flagellar assembly state via FlgM sequestration and export, a mechanism that ensures late genes are transcribed primarily after assembly has progressed. (leal‐morales2022transcriptionalorganizationand pages 14-14, xiao2017expressionofthe pages 1-2)
While not FliA itself, upstream master regulation shapes when fliA is expressed: FleQ ChIP-seq in KT2440 identified 103 putative FleQ binding sites, supporting FleQ as a broad regulator upstream of σ54-dependent class II genes that include fliA. (blancoromero2018genomewideanalysisof pages 1-2)
Direct industrial applications of P. putida KT2440 commonly leverage its metabolism and robustness; however, motility control is practically important in environmental and engineered contexts because it affects surface colonization, biofilm formation, and dispersal. In the KT2440 system, FliA is a key transcriptional node controlling late motility outputs and also modulates bifA/c-di-GMP, meaning that perturbing fliA (deletion or overexpression) can be used experimentally to:
- Disable or enhance swimming motility (ΔfliA nonmotile; FliA overexpression enhances swimming in a BifA-dependent manner). (xiao2017expressionofthe pages 4-5, xiao2017expressionofthe pages 8-9)
- Tune expression from σ28 promoters (e.g., engineered reporters or synthetic control elements based on σ28 motifs identified in the flagellar cluster). (leal‐morales2022transcriptionalorganizationand pages 6-6, leal‐morales2022transcriptionalorganizationand media ffe1d522)
These applications are most mature as research and synthetic biology strategies (motility/biofilm tuning and promoter engineering) rather than direct deployed products.
Checkpointed transcription ensures cost-effective assembly. The FlgM-mediated sequestration mechanism ties FliA activity to structural completion of the hook–basal body, preventing premature expression of filament/late genes. This is described explicitly for P. putida and synthesized in recent expert reviews for pseudomonads. (leal‐morales2022transcriptionalorganizationand pages 14-14, oladosu2024fliptheswitch pages 3-4)
FliA is a regulatory hub with feedback architecture. In P. putida, FliA promotes expression of flgM (negative feedback) and can drive transcription of upstream regulators (e.g., fleQ and fleSR as part of a larger operon), forming feed-forward/feedback loops that can stabilize a motility program once initiated. (leal‐morales2022transcriptionalorganizationand pages 14-14)
Beyond canonical flagellar genes, FliA can couple motility and second-messenger signaling. In KT2440, FliA partly controls bifA, linking σ28 control to c-di-GMP turnover and swimming behavior. (xiao2017expressionofthe pages 5-7, xiao2017expressionofthe pages 8-9)
The following table compiles the most relevant KT2440-specific evidence and recent reviews used to support functional annotation and quantitative claims.
| Source | Year/date | URL / DOI | Evidence type | Main findings | Scope / notes |
|---|---|---|---|---|---|
| Leal-Morales et al., Environmental Microbiology | Dec 2022 | https://doi.org/10.1111/1462-2920.15857 | Genetic regulation mapping, promoter architecture, operon analysis | In P. putida KT2440, the flagellar cluster contains 59 genes, organized into 11 operons with 22 primary/internal promoters; the system follows a three-tier cascade in which FleQ is Class I, FleQ+σ54 control Class II genes including fliA, and FliA (σ28) activates Class III genes needed for filament synthesis, one stator, and chemotaxis completion (leal‐morales2022transcriptionalorganizationand pages 1-1). Promoter analysis identified 21 putative flagellar promoters overall, including FliA-dependent motifs upstream of fliK2, fliC, cheV, fliS, flgM; σ54-type motifs were found upstream of several earlier flagellar operons (leal‐morales2022transcriptionalorganizationand pages 6-6). The paper also describes FliA as central to feed-forward/feedback control: FliA activates late genes and promotes flgM expression, while hook completion enables FlgM export and FliA release (leal‐morales2022transcriptionalorganizationand pages 14-14, leal‐morales2022transcriptionalorganizationand media 34a91b68). | KT2440-specific primary study; strongest source for operon counts, promoter classes, and regulatory hierarchy. |
| Xiao et al., MicrobiologyOpen | Sep 2017 | https://doi.org/10.1002/mbo3.402 | Genetics, promoter-lacZ assays, 5′-RACE, qRT-PCR, c-di-GMP biochemistry | Demonstrated that FliA partly controls bifA expression in P. putida KT2440: fliA deletion lowered bifA transcription about twofold and caused a nonmotile phenotype that was complemented by plasmid-borne fliA (xiao2017expressionofthe pages 4-5, xiao2017expressionofthe pages 1-2). 5′-RACE identified two bifA TSSs at 103 nt and 40 nt upstream of the start codon, with upstream σ70 and σ28 promoter elements; mutation of the σ28 promoter reduced activity, and FliA overexpression in an E. coli reporter increased activity about fivefold (xiao2017expressionofthe pages 5-7). Reported intracellular c-di-GMP values were 23.33 pmol/mg protein in WT vs 20.13 pmol/mg in the fliA mutant; FliA overexpression promoted swimming in a BifA-dependent manner (xiao2017expressionofthe pages 5-7, xiao2017expressionofthe pages 8-9). | KT2440-specific primary study; strongest source for direct quantitative phenotypes, dual-promoter architecture at bifA, and c-di-GMP linkage. |
| Blanco-Romero et al., Scientific Reports | Sep 2018 | https://doi.org/10.1038/s41598-018-31371-z | ChIP-seq, regulon mapping (FleQ) | Defined upstream hierarchy around FliA by showing that FleQ is the master regulator of pseudomonad flagellar transcription and identified 103 putative FleQ binding sites in P. putida KT2440. FleQ works with σ54/RpoN to activate multiple early flagellar operons, including loci that feed into the layer containing fliA (blancoromero2018genomewideanalysisof pages 1-2). | KT2440-specific primary study, but focuses on FleQ, not direct FliA targets; useful for upstream regulatory context. |
| Oladosu et al., Journal of Bacteriology | Mar 2024 | https://doi.org/10.1128/jb.00365-23 | Expert review | Summarizes authoritative current understanding in pseudomonads: FliA is constitutively expressed but post-translationally sequestered by FlgM; after hook-basal body completion, FlgM export frees FliA, enabling late/class IV transcription such as fliC, fleL, cheAB, motAB, cheW, cheVR, flgMN, cheYZ. The review also highlights integration of the FliA/FlgM module with broader signaling and c-di-GMP-linked lifestyle regulation (oladosu2024fliptheswitch pages 3-4). | Cross-species Pseudomonas review centered on P. aeruginosa; used for conserved mechanistic interpretation, not KT2440-specific claims. |
| Lo et al., PLoS ONE | May 2016 | https://doi.org/10.1371/journal.pone.0155397 | Transcriptomics, reporter assays, phenotype analysis | Provides cross-species evidence that FliA regulates more than canonical flagellar genes: in P. aeruginosa, FliA affected expression of phosphodiesterase genes such as PA4367/bifA, linking FliA to c-di-GMP metabolism, swarming, and pigment production. The study also notes that excess FliA can trigger feedback through flgM, supporting careful dosage control of σ28 activity (lo2016regulationofmotility pages 11-14, lo2016regulationofmotility pages 14-15). | Cross-species primary study; not KT2440-specific, but supports broader interpretation of FliA as a motility–c-di-GMP network node. |
Table: This table compiles the key KT2440-specific and comparative Pseudomonas evidence for FliA (sigma-28), including regulatory hierarchy, promoter architecture, quantitative measurements, and broader expert interpretation. It is useful for separating direct evidence in P. putida KT2440 from conserved mechanisms inferred from related pseudomonads.
References
(leal‐morales2022transcriptionalorganizationand pages 1-1): Antonio Leal‐Morales, Marta Pulido‐Sánchez, Aroa López‐Sánchez, and Fernando Govantes. Transcriptional organization and regulation of the pseudomonas putida flagellar system. Environmental Microbiology, 24:137-157, Dec 2022. URL: https://doi.org/10.1111/1462-2920.15857, doi:10.1111/1462-2920.15857. This article has 31 citations and is from a domain leading peer-reviewed journal.
(leal‐morales2022transcriptionalorganizationand pages 14-14): Antonio Leal‐Morales, Marta Pulido‐Sánchez, Aroa López‐Sánchez, and Fernando Govantes. Transcriptional organization and regulation of the pseudomonas putida flagellar system. Environmental Microbiology, 24:137-157, Dec 2022. URL: https://doi.org/10.1111/1462-2920.15857, doi:10.1111/1462-2920.15857. This article has 31 citations and is from a domain leading peer-reviewed journal.
(xiao2017expressionofthe pages 5-7): Yujie Xiao, Huizhong Liu, Hailing Nie, Shan Xie, Xuesong Luo, Wenli Chen, and Qiaoyun Huang. Expression of the phosphodiesterase bifa facilitating swimming motility is partly controlled by flia in pseudomonas putida kt2440. MicrobiologyOpen, 6:e00402, Sep 2017. URL: https://doi.org/10.1002/mbo3.402, doi:10.1002/mbo3.402. This article has 16 citations and is from a peer-reviewed journal.
(xiao2017expressionofthe pages 4-5): Yujie Xiao, Huizhong Liu, Hailing Nie, Shan Xie, Xuesong Luo, Wenli Chen, and Qiaoyun Huang. Expression of the phosphodiesterase bifa facilitating swimming motility is partly controlled by flia in pseudomonas putida kt2440. MicrobiologyOpen, 6:e00402, Sep 2017. URL: https://doi.org/10.1002/mbo3.402, doi:10.1002/mbo3.402. This article has 16 citations and is from a peer-reviewed journal.
(leal‐morales2022transcriptionalorganizationand media 34a91b68): Antonio Leal‐Morales, Marta Pulido‐Sánchez, Aroa López‐Sánchez, and Fernando Govantes. Transcriptional organization and regulation of the pseudomonas putida flagellar system. Environmental Microbiology, 24:137-157, Dec 2022. URL: https://doi.org/10.1111/1462-2920.15857, doi:10.1111/1462-2920.15857. This article has 31 citations and is from a domain leading peer-reviewed journal.
(oladosu2024fliptheswitch pages 3-4): Victoria I. Oladosu, Soyoung Park, and Karin Sauer. Flip the switch: the role of fleq in modulating the transition between the free-living and sessile mode of growth in pseudomonas aeruginosa. Journal of Bacteriology, Mar 2024. URL: https://doi.org/10.1128/jb.00365-23, doi:10.1128/jb.00365-23. This article has 27 citations and is from a peer-reviewed journal.
(sanchezjimenez2023transcriptionalregulatorscontrolling pages 18-19): Ana Sánchez-Jiménez, María A. Llamas, and Francisco Javier Marcos-Torres. Transcriptional regulators controlling virulence in pseudomonas aeruginosa. International Journal of Molecular Sciences, 24:11895, Jul 2023. URL: https://doi.org/10.3390/ijms241511895, doi:10.3390/ijms241511895. This article has 64 citations.
(sanchezjimenez2023transcriptionalregulatorscontrolling pages 19-21): Ana Sánchez-Jiménez, María A. Llamas, and Francisco Javier Marcos-Torres. Transcriptional regulators controlling virulence in pseudomonas aeruginosa. International Journal of Molecular Sciences, 24:11895, Jul 2023. URL: https://doi.org/10.3390/ijms241511895, doi:10.3390/ijms241511895. This article has 64 citations.
(leal‐morales2022transcriptionalorganizationand pages 6-6): Antonio Leal‐Morales, Marta Pulido‐Sánchez, Aroa López‐Sánchez, and Fernando Govantes. Transcriptional organization and regulation of the pseudomonas putida flagellar system. Environmental Microbiology, 24:137-157, Dec 2022. URL: https://doi.org/10.1111/1462-2920.15857, doi:10.1111/1462-2920.15857. This article has 31 citations and is from a domain leading peer-reviewed journal.
(leal‐morales2022transcriptionalorganizationand media ffe1d522): Antonio Leal‐Morales, Marta Pulido‐Sánchez, Aroa López‐Sánchez, and Fernando Govantes. Transcriptional organization and regulation of the pseudomonas putida flagellar system. Environmental Microbiology, 24:137-157, Dec 2022. URL: https://doi.org/10.1111/1462-2920.15857, doi:10.1111/1462-2920.15857. This article has 31 citations and is from a domain leading peer-reviewed journal.
(xiao2017expressionofthe pages 1-2): Yujie Xiao, Huizhong Liu, Hailing Nie, Shan Xie, Xuesong Luo, Wenli Chen, and Qiaoyun Huang. Expression of the phosphodiesterase bifa facilitating swimming motility is partly controlled by flia in pseudomonas putida kt2440. MicrobiologyOpen, 6:e00402, Sep 2017. URL: https://doi.org/10.1002/mbo3.402, doi:10.1002/mbo3.402. This article has 16 citations and is from a peer-reviewed journal.
(xiao2017expressionofthe pages 8-9): Yujie Xiao, Huizhong Liu, Hailing Nie, Shan Xie, Xuesong Luo, Wenli Chen, and Qiaoyun Huang. Expression of the phosphodiesterase bifa facilitating swimming motility is partly controlled by flia in pseudomonas putida kt2440. MicrobiologyOpen, 6:e00402, Sep 2017. URL: https://doi.org/10.1002/mbo3.402, doi:10.1002/mbo3.402. This article has 16 citations and is from a peer-reviewed journal.
(blancoromero2018genomewideanalysisof pages 1-2): Esther Blanco-Romero, Miguel Redondo-Nieto, Francisco Martínez-Granero, Daniel Garrido-Sanz, Maria Isabel Ramos-González, Marta Martín, and Rafael Rivilla. Genome-wide analysis of the fleq direct regulon in pseudomonas fluorescens f113 and pseudomonas putida kt2440. Scientific Reports, Sep 2018. URL: https://doi.org/10.1038/s41598-018-31371-z, doi:10.1038/s41598-018-31371-z. This article has 64 citations and is from a peer-reviewed journal.
(lo2016regulationofmotility pages 11-14): Yi-Ling Lo, Lunda Shen, Chih-Hsuan Chang, Manish Bhuwan, Cheng-Hsun Chiu, and Hwan-You Chang. Regulation of motility and phenazine pigment production by flia is cyclic-di-gmp dependent in pseudomonas aeruginosa pao1. PLoS ONE, 11:e0155397, May 2016. URL: https://doi.org/10.1371/journal.pone.0155397, doi:10.1371/journal.pone.0155397. This article has 46 citations and is from a peer-reviewed journal.
(lo2016regulationofmotility pages 14-15): Yi-Ling Lo, Lunda Shen, Chih-Hsuan Chang, Manish Bhuwan, Cheng-Hsun Chiu, and Hwan-You Chang. Regulation of motility and phenazine pigment production by flia is cyclic-di-gmp dependent in pseudomonas aeruginosa pao1. PLoS ONE, 11:e0155397, May 2016. URL: https://doi.org/10.1371/journal.pone.0155397, doi:10.1371/journal.pone.0155397. This article has 46 citations and is from a peer-reviewed journal.