Gene Ontology annotation through association of InterPro records with GO terms
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InterPro terpene-synthase-family domain mappings (IPR001906, IPR036965, IPR050148) assign terpene synthase activity, terpenoid biosynthetic process and lyase activity to OsCPS4.
Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
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SwissProt keyword-derived (SPKW) annotations present in the Sept 2025 goa_uniprot_gcrp snapshot but removed from the current GOA release after GOA retired the keyword2GO pipeline for cellular organisms.
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For CPS4 the keyword "Plant defense" mapped to the broad "defense response" process, conflating the protective role of the downstream phytoalexin products with the catalytic function of the biosynthetic enzyme; removal was justified.
Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt
Electronic Gene Ontology annotations created by ARBA machine learning models
Combined Automated Annotation using Multiple IEA Methods
Functional identification of rice syn-copalyl diphosphate synthase and its role in initiating biosynthesis of diterpenoid phytoalexin/allelopathic natural products.
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Functionally identified OsCPSsyn (OsCPS4) by recombinant expression and functional analysis as the class II terpene synthase converting GGPP to syn-CPP, the committed step in biosynthesis of rice phytoalexins/allelopathic products.
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syn-CPP is the only known metabolic fate of this compound in rice; OsCPSsyn mRNA is specifically induced by conditions that stimulate phytoalexin biosynthesis.
Biological functions of ent- and syn-copalyl diphosphate synthases in rice: key enzymes for the branch point of gibberellin and phytoalexin biosynthesis.
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Demonstrated by bacterial expression that OsCyc1 (= OsCPS4) encodes syn-CDP synthase, while OsCyc2 and OsCPS1 encode ent-CDP synthase, defining the syn/ent diterpenoid branch point.
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OsCyc1/OsCyc2 transcripts are strongly induced by UV; OsCyc1 products feed momilactones A/B and oryzalexin S (syn branch).
Reverse-genetic approach to verify physiological roles of rice phytoalexins: characterization of a knockdown mutant of OsCPS4 phytoalexin biosynthetic gene in rice.
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An OsCPS4 knockdown mutant has decreased momilactones and oryzalexin S, increased susceptibility to the rice blast fungus, and reduced capacity to inhibit lowland weeds in paddy soil - establishing that OsCPS4's defense/allelopathy relevance is mediated by its phytoalexin products.
Deep-research report (falcon / Edison Scientific Literature) - functional annotation of rice CPS4 / OsCPS4 / OsCyc1 (Q0JF02).
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Synthesizes the primary literature (Xu et al. 2004 PMID:15255861; Otomo et al. 2004 PMID:15341631; Toyomasu et al. 2014 PMID:23621683; Lu et al. 2018; Ma et al. 2023; Morrone et al. 2011) concluding OsCPS4/OsCyc1 is a class II diterpene cyclase (syn-copalyl diphosphate synthase, EC 5.5.1.14) that converts GGPP to syn-CPP, the committed branch-point intermediate.
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syn-CPP made by OsCPS4 feeds the syn-CPP branch leading to momilactones A/B and oryzalexin S - the best-established metabolic fates of syn-CPP in rice, linked to phytoalexin and allelopathic functions; OsCPS4 is a specialized-metabolism gatekeeper rather than a primary- metabolism enzyme.
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CPS4 is part of the rice momilactone biosynthetic gene cluster (MBGC) on chromosome 4, with downstream KSL4 performing the first dedicated cyclization toward momilactones.
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2023 X-ray/cryo-EM structural work on OsCyc1/OsCPS4 defined active-site geometry underlying syn-stereochemistry; the enzyme is active independent of its dominant tetrameric oligomeric state, and rational mutagenesis can expand product outcome to include ent-CPP.
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Localization is database-supported (UniProt chloroplastic precursor, plastidial GGPP-based diterpenoid biosynthesis) rather than directly demonstrated for this protein in the retrieved literature.