HSK, also called DMR1, is a chloroplast homoserine kinase that uses Mg-ATP to generate O-phosphohomoserine. This metabolite supplies both threonine synthase and the cystathionine gamma-synthase branch toward methionine. HSK activity and homoserine availability influence amino-acid metabolism; reduced-function alleles accumulate homoserine and alter susceptibility to downy mildew and certain fungal pathogens in tissue- and allele-dependent ways.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004413 homoserine kinase activity | IDA PMID:15703056 Methionine and threonine synthesis are limited by homoserine... | ACCEPT | Summary: HSK catalyzes ATP-dependent homoserine phosphorylation. Reason: Purified recombinant HSK uses L-homoserine and Mg-ATP, with measured substrate dependence. ATP binding is integral to the kinase mechanism. Supporting Evidence: PMID:10562426 The apparent K(m) values are 0.40 mM for l-homoserine and 0.32 mM for Mg-ATP. |
| GO:0004413 homoserine kinase activity | IEA GO_REF:0000120 | ACCEPT | Summary: HSK catalyzes ATP-dependent homoserine phosphorylation. Reason: Purified recombinant HSK uses L-homoserine and Mg-ATP, with measured substrate dependence. ATP binding is integral to the kinase mechanism. Supporting Evidence: PMID:10562426 The apparent K(m) values are 0.40 mM for l-homoserine and 0.32 mM for Mg-ATP. |
| GO:0005524 ATP binding | IEA GO_REF:0000002 | ACCEPT | Summary: HSK catalyzes ATP-dependent homoserine phosphorylation. Reason: Purified recombinant HSK uses L-homoserine and Mg-ATP, with measured substrate dependence. ATP binding is integral to the kinase mechanism. Supporting Evidence: PMID:10562426 The apparent K(m) values are 0.40 mM for l-homoserine and 0.32 mM for Mg-ATP. |
| GO:0006566 L-threonine metabolic process | IEA GO_REF:0000002 | MODIFY | Summary: Specify the supported threonine biosynthetic contribution. Reason: HSK generates the O-phosphohomoserine consumed by threonine synthase; this is a synthetic step, already represented by GO:0009088, rather than threonine degradation. Proposed replacements: L-threonine biosynthetic process Supporting Evidence: |
| GO:0009088 L-threonine biosynthetic process | IEA GO_REF:0000041 | ACCEPT | Summary: Plant HSK supplies a shared precursor for both threonine and methionine. Reason: PMID:15703056 explicitly identifies O-phosphohomoserine as substrate for TS and CGS. HSK executes the common phosphorylation step and is not an exclusive threonine commitment enzyme; limited response to overexpression does not negate its role. Supporting Evidence: PMID:15703056 Homoserine kinase (HSK) produces O-phospho-l-homoserine (HserP) used by cystathionine gamma-synthase (CGS) for Met synthesis and threonine synthase (TS) for Thr synthesis. |
| GO:0009088 L-threonine biosynthetic process | TAS PMID:15703056 Methionine and threonine synthesis are limited by homoserine... | ACCEPT | Summary: Plant HSK supplies a shared precursor for both threonine and methionine. Reason: PMID:15703056 explicitly identifies O-phosphohomoserine as substrate for TS and CGS. HSK executes the common phosphorylation step and is not an exclusive threonine commitment enzyme; limited response to overexpression does not negate its role. Supporting Evidence: PMID:15703056 Homoserine kinase (HSK) produces O-phospho-l-homoserine (HserP) used by cystathionine gamma-synthase (CGS) for Met synthesis and threonine synthase (TS) for Thr synthesis. |
| GO:0009507 chloroplast | HDA PMID:18431481 Sorting signals, N-terminal modifications and abundance of t... | MODIFY | Summary: The supported enzymatic compartment is chloroplast stroma. Reason: Primary PMID:18431481 exact-target supplementary tables detect AT2G17265.1 in chloroplast and stromal preparations; existing AT_CHLORO annotations and curated target localization corroborate this assignment. The cross-gene source extraction preserves peptide/protein counts and source table identities rather than using the GOA annotation as evidence. Proposed replacements: chloroplast stroma Supporting Evidence: file:ARATH/TS1/TS1-source-analysis/localization-table-extraction.json AT2G17265.1 |
| GO:0009507 chloroplast | ISM GO_REF:0000122 | MODIFY | Summary: The supported enzymatic compartment is chloroplast stroma. Reason: Primary PMID:18431481 exact-target supplementary tables detect AT2G17265.1 in chloroplast and stromal preparations; existing AT_CHLORO annotations and curated target localization corroborate this assignment. The cross-gene source extraction preserves peptide/protein counts and source table identities rather than using the GOA annotation as evidence. Proposed replacements: chloroplast stroma Supporting Evidence: file:ARATH/TS1/TS1-source-analysis/localization-table-extraction.json AT2G17265.1 |
| GO:0009570 chloroplast stroma | HDA PMID:20061580 AT_CHLORO, a comprehensive chloroplast proteome database wit... | ACCEPT | Summary: The supported enzymatic compartment is chloroplast stroma. Reason: Primary PMID:18431481 exact-target supplementary tables detect AT2G17265.1 in chloroplast and stromal preparations; existing AT_CHLORO annotations and curated target localization corroborate this assignment. The cross-gene source extraction preserves peptide/protein counts and source table identities rather than using the GOA annotation as evidence. Supporting Evidence: file:ARATH/TS1/TS1-source-analysis/localization-table-extraction.json AT2G17265.1 |
| GO:0009570 chloroplast stroma | IDA PMID:15703056 Methionine and threonine synthesis are limited by homoserine... | ACCEPT | Summary: The supported enzymatic compartment is chloroplast stroma. Reason: Primary PMID:18431481 exact-target supplementary tables detect AT2G17265.1 in chloroplast and stromal preparations; existing AT_CHLORO annotations and curated target localization corroborate this assignment. The cross-gene source extraction preserves peptide/protein counts and source table identities rather than using the GOA annotation as evidence. Supporting Evidence: file:ARATH/TS1/TS1-source-analysis/localization-table-extraction.json AT2G17265.1 |
| GO:0009570 chloroplast stroma | IEA GO_REF:0000044 | ACCEPT | Summary: The supported enzymatic compartment is chloroplast stroma. Reason: Primary PMID:18431481 exact-target supplementary tables detect AT2G17265.1 in chloroplast and stromal preparations; existing AT_CHLORO annotations and curated target localization corroborate this assignment. The cross-gene source extraction preserves peptide/protein counts and source table identities rather than using the GOA annotation as evidence. Supporting Evidence: file:ARATH/TS1/TS1-source-analysis/localization-table-extraction.json AT2G17265.1 |
| GO:0009617 response to bacterium | IGI PMID:15986928 Identification of arabidopsis loci required for susceptibili... | MARK AS OVER ANNOTATED | Summary: The tested bacterial infection does not establish a HSK response function. Reason: The source PMID:15986928 Results/Fig5 reports unchanged bacterial susceptibility of dmr1, unlike resistant dmr3/4; full PMID:19622802 likewise distinguishes downy-mildew specificity from Pseudomonas susceptibility. Normal infection in a mutant is not positive participation evidence for this response. This assessment does not claim that every possible bacterial context is excluded. Supporting Evidence: PMID:19622802 resistant to H. arabidopsidis but susceptible to infection by other pathogens |
| GO:0009620 response to fungus | IGI PMID:15986928 Identification of arabidopsis loci required for susceptibili... | KEEP AS NON CORE | Summary: HSK-dependent metabolism affects fungal susceptibility in defined contexts. Reason: The original2005 source emphasizes oomycete resistance and mixed powdery-mildew alleles, but later direct PMID:25432266 tests multiple HSK mutants against Fusarium. Leaf/silique effects depend on allele and tissue, while floral effects differ. Retain the precise fungal-response claim as a peripheral metabolic phenotype, without inventing a pathogen receptor or general immune activation. Supporting Evidence: |
| GO:0048573 photoperiodism, flowering | IMP PMID:15740643 Characterization of a novel developmentally retarded mutant ... | REMOVE | Summary: The cited flowering mutant is a different mapped locus. Reason: The full author reproduction of PMID:15740643 (mapping Results and Discussion) identifies developmentally retarded DRM1 near MXK3.1 on chromosome 5, with causal gene identification still pending. HSK/downy-mildew-resistant DMR1 is At2g17265 on chromosome 2, established by PMID:19622802. The flowering annotation conflates distinct similarly named mutants; this conclusion follows full-text inspection, not title-only inference. Supporting Evidence: PMID:15740643 which was mapped to the bottom of chromosome 5 PMID:19622802 DMR1 Encodes HSK |
| GO:0071265 L-methionine biosynthetic process | TAS PMID:15703056 Methionine and threonine synthesis are limited by homoserine... | ACCEPT | Summary: Plant HSK supplies a shared precursor for both threonine and methionine. Reason: PMID:15703056 explicitly identifies O-phosphohomoserine as substrate for TS and CGS. HSK executes the common phosphorylation step and is not an exclusive threonine commitment enzyme; limited response to overexpression does not negate its role. Supporting Evidence: PMID:15703056 Homoserine kinase (HSK) produces O-phospho-l-homoserine (HserP) used by cystathionine gamma-synthase (CGS) for Met synthesis and threonine synthase (TS) for Thr synthesis. |
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Experiment: Combine endogenous localization and fraction purity controls with isotope tracing and matched purified-enzyme substrate/cofactor measurements; distinguish shared precursor supply, net flux and secondary developmental or pathogen phenotypes.
Type: compartment-resolved isotope flux and enzyme kinetics
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