plo1 (Polo-like kinase, S. pombe) — review notes

UniProt: P50528. PomBase: SPAC23C11.16. Sole Polo-like kinase (PLK) of fission yeast.
Architecture: N-terminal Ser/Thr protein kinase domain (aa 41-296; ATP binding 47-55, K69; catalytic Asp/proton acceptor 163) and C-terminal Polo-box domain composed of POLO box 1 (493-575) and POLO box 2 (596-678). The polo boxes form a single functional substrate-targeting module.

Core function summary

Master mitotic regulator. Ser/Thr kinase activity is biochemically demonstrated. Localizes to SPB (mitotic only), mitotic spindle, spindle midzone, kinetochore, division-site/contractile ring, and (in meiosis) meiotic SPB/spindle/poles and kinetochore. Drives mitotic commitment (positive feedback on Cdc25/MPF via Cut12 at the SPB), bipolar spindle formation, contractile-ring/medial-ring assembly (via Mid1), and septation (initiates SIN). In meiosis (via Moa1/meikin) directs mono-orientation and cohesion protection (Rec8 phosphorylation).

Key findings with provenance

Catalytic / kinase activity

• PMID:11250892 — kinase activity, mitotic peak.
• PMID:22375062 — Ser/Thr kinase activity (direct substrate Dam1).
• PMID:33888556 — direct in vitro Ser/Thr kinase activity.
• Kinase-dead K69R/K69Q loss of function [UniProt MUTAGEN 69].

Mitotic commitment / G2-M / SPB recruitment

• [PMID:12815070 title "Physical and functional interactions between polo kinase and the spindle pole component Cut12 regulate mitotic commitment in S. pombe."] — Cut12 interaction; mitotic commitment.
• PMID:15917811 — links stress pathway to G2-M and cell size/tip growth; intracellular signal transduction.
• PMID:21965528 — Aurora drives Plo1 to SPB promoting G2-M; mitotic SPB localization.
• PMID:23333317 — Plo1-Cut12 binding (SPBC649.05 = cut12).
• PMID:10436027 — mitotic SPB localization.
• PMID:34133218 — direct SIM and chemical-genetic support for Plo1 at the nuclear-facing SPB and for its role in localized NE breakdown/SPB insertion. The authors explicitly state that direct phosphorylation of Sad1 has not been detected, so the substrate remains unresolved.
• PMID:21131906 — Dma1-dependent Sid4 ubiquitination controls the timing of Plo1 recruitment during checkpoint arrest; this paper supports regulated SPB recruitment, while Plo1 kinase activity is established more directly by the assays cited above.

Spindle / spindle organization

• PMID:7744248 — required for bipolar spindle formation.
• PMID:11250892 Plo1 localizes to mitotic spindle (IDA). PMID:9852154 "Plo1p localizes to the spindle pole bodies and spindles of mitotic cells and also to the medial ring".

Contractile ring / cytokinesis / septation

• PMID:7744248 — actin ring + septum.
• PMID:21376600 — contractile ring assembly via Mid1/anillin; EXP for regulation of actomyosin ring assembly.
• PMID:11250892 — SIN; positive regulation of septation initiation signaling.
• PMID:24920823 and "Cdk1-mediated phosphoregulation of Byr4 facilitates complete removal of Byr4 from metaphase SPBs in concert with Plo1" — SIN activation.
• [PMID:9852154 "Plo1p is thus implicated as a key molecule in the spatial and temporal coordination of cytokinesis with mitosis." / "Plo1p is required for Mid1p to exit the nucleus and form a ring"] — division-site selection; Mid1 nuclear export; nucleus/spindle midzone localization; cytokinesis.
• PMID:25356547 — ESCRT interactions (SPAC1142.07c, SPAC1B3.07c, SPBC215.14c are ESCRT genes); septation/membrane trafficking.

APC / metaphase-anaphase

• PMID:11777938 — Cut23(Apc8) interaction (SPAC6F12.14 = cut23); metaphase/anaphase transition.

Transcription

• PMID:12411492 — positive regulation of M-G1 transcription (PolII).

Meiosis

• PMID:25533956 — Plo1/Moa1 mono-orientation + cohesion protection; kinetochore.
• PMID:28497540 — meiotic Bub1 distribution/cohesion protection.
• PMID:33888556 — cohesion protection in anaphase I via Rec8-S450.
• PMID:38448160 — mono-orientation (homologous chromosome orientation in metaphase I).
• PMID:22438582 — meiotic SPB organization/remodeling; meiotic SPB localization.
• PMID:23770679 — meiotic centromere clustering / kinetochore retrieval; kinetochore localization; kinase activity.
• PMID:20826461 dma1 in spore formation; Plo1 listed as IDA for meiotic spindle/meiotic spindle pole. Abstract is about dma1 but PomBase curated Plo1 meiotic spindle/pole localization from full text (defer to curator).

Localization (large-scale / phosphoproteomics)

• PMID:16823372 ORFeome global localization — cytoplasm/cytosol/SPB (HDA).
• PMID:33176152 — Plo1 sequestered into nucleolar inclusion bodies under heat stress; reversible aggregation, NOT a normal functional location.
• PMID:25487150 — Plo1 IDA kinase activity in mitotic-progression context.

Curation considerations

• "protein binding" (GO:0005515) IPI annotations: not informative MF; mark over-annotated (the interactions themselves — Cut12, Cut23, Mid1, ESCRT, Moa1 — are real and underpin BP terms).
• nucleolar peripheral inclusion body (PMID:33176152): real IDA localization but it is a stress-induced aggregation site, not a site of normal function — keep as non-core.
• IEA terms (protein kinase activity, ATP binding, Ser kinase activity, nucleus, SPB) are supported by experimental data; generally ACCEPT (ATP binding, Ser kinase) or note redundancy.
• Defer to PomBase curators on all IDA/IMP/IPI/IGI experimental annotations per project rules.
• The 2026 GOA refresh added PMID:34133218 annotations to the half bridge, inner plaque, and mitotic SPB insertion. Accept all three: the full text directly places the bulk Plo1 signal at the INM/nuclear face and shows that acute Plo1 inhibition disrupts ring remodeling and insertion. Do not infer a direct Sad1 substrate relationship; the paper says this has not been detected.

2026-09-01 research refresh

• The project wrapper refreshed 76 GOA rows and added four new annotations: an IDA kinase annotation from PMID:21131906 and three PMID:34133218 annotations covering the half bridge, inner plaque, and mitotic SPB insertion. All were manually reviewed; no PENDING actions remain.
• OpenScientist tested the focused hypothesis that Plo1 directly phosphorylates an SPB-ring component. It judged the process claim supported but the direct-substrate clause unresolved, agreeing with the full-text statement that direct Sad1 phosphorylation has not been detected. This constrained the core-function wording and generated a substrate-identification experiment rather than a new MF assertion.
• Falcon's broader synthesis corroborated the existing core modules and highlighted the unusually direct meiotic Rec8/Psm3 substrate evidence. It is retained as research provenance, while annotation decisions cite the cached primary literature.
• Meiosis is kept outside core_functions despite the unusually direct Rec8/Psm3 substrate evidence because it is a stage-specific deployment of the same Plo1 kinase rather than the constitutive organizing role that makes Plo1 essential in vegetative M phase. The individual meiotic annotations remain retained as non-core, not discounted or removed.

2026-11-01 PMID:23222840 integration (Grallert et al. 2013, Nat Cell Biol)

Cached text: abstract plus PMC author-manuscript main text (results and discussion). Figure legends, methods and supplementary figures are NOT in the cache; claims below rest on the main-text narrative.

• Late-G2 SPB recruitment and activity: PMID:23222840; FRAP half-life 21-22 s; MPM2 SPB staining is Plo1-dependent and reports local Plo1 activity.
• MPF dependency: PMID:23222840 (cdc2.as + 1NA-PP1; washout restores Plo1 at the SPB).
• Mitotic-commitment timing (loss of function): PMID:23222840. plo1.as8 = M→F gatekeeper-region change in a plo1.as3 backbone; strong inhibition gives monopolar spindles.
• SPB-tethered active Plo1 (GBP chimera Plo1.RL): PMID:23222840; requires functional endogenous Plo1 (fails in plo1.ts41).
• SPB-tethered Cdc2.RL acts through Plo1: PMID:23222840
• NETO: coincident with Plo1 SPB recruitment ("every post-NETO G2 cell displayed a Plo1.GFP signal at its SPB while neighbouring pre-NETO cells had none"); PMID:23222840; PMID:23222840; PMID:23222840 MPF-induced NETO also needs Tea1, Bud6 and Sla2.

Curation decisions:
- Added the reference with findings and reference_review (HIGH/VERIFIED).
- GO:0010971 (positive regulation of G2/M transition, IMP PMID:21965528 row) gains PMID:23222840 supporting quotes; no new G2/M row (term already carried twice by IMP).
- SPB localization: no new CC row; GO:0044732 mitotic SPB / GO:0005816 SPB already carried, and the late-G2 SPB is part of the vegetative (mitotic-cycle) SPB.
- NEW GO:0051523 "cell growth mode switching, monopolar to bipolar" (IMP, PMID:23222840). Term choice: GO:0051519 activation of bipolar cell growth is obsolete; GO:0051518 positive regulation of bipolar cell growth is the alternative, but GO:0051523 names the NETO switch itself and sits under regulation of direction of cell growth. Comparator check (QuickGO, S. pombe): GO:0051523 is carried by IMP for signalling regulators of NETO such as ssp1, kin1, rgf1, tea3, so a regulatory kinase is the conventional bearer. Kept out of core_functions (single paper; downstream targets unknown), but mentioned in description.
- Core function 2 (mitotic commitment) description extended with MPF-dependent late-G2 SPB activation, with two PMID:23222840 quotes.
- cdc2 review: NEW GO:0051523 for cdc2 too (IMP: strong cdc2.as inhibition blocks NETO; SPB-tethered Cdc2.RL triggers NETO, Plo1-dependent).