BAS1 (Biotrophy-associated secreted protein 1, MGG_04795) is a small (115 aa), cysteine-free secreted protein of the rice blast fungus Magnaporthe oryzae (Pyricularia oryzae) with no recognizable domains, paralogs or orthologs. Its gene is among the most strongly induced in biotrophic invasive hyphae inside living rice cells. BAS1 is a cytoplasmic effector: it is secreted by invasive hyphae through a Brefeldin A-insensitive, exocyst- and Sso1 t-SNARE-dependent route into the biotrophic interfacial complex (BIC), a plant membrane-rich structure lying outside the fungal plasma membrane, and is then translocated into the cytoplasm of the invaded rice cell, a step that is blocked by inhibitors of host clathrin-mediated endocytosis. Fluorescent BAS1 also moves from invaded cells into uninvaded neighbouring rice cells. Accumulation is characteristic of compatible interactions. Its biochemical activity and host targets are unknown; BAS1 deletion mutants show at most minor, inconsistent reductions in lesion number and size. BAS1 fluorescent fusions are widely used as a reporter of BIC-directed effector secretion and translocation.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005576 extracellular region | EXP PMID:19357089 Interaction transcriptome analysis identifies Magnaporthe or... | ACCEPT | Summary: Mosquera et al. (2009) showed by live-cell imaging that BAS1:EYFP is secreted by invasive hyphae into biotrophic interfacial complexes (BICs), failing to colocalize with a fungal cytoplasmic marker but colocalizing with the BIC effector AVR-Pita1. Giraldo et al. (2013) showed the BIC lies outside the fungal plasma membrane. Reason: Direct imaging evidence of secretion out of the fungal cell. The BIC is a transit compartment on the way to the host cytoplasm, so this is a correct but non-terminal location; no GO cellular component term exists for the BIC, and extracellular region is the appropriate available term. Supporting Evidence: PMID:19357089 Therefore, BAS1 encodes a small unique protein that is secreted into BICs. PMID:23774898 confirming that the BIC lies outside the fungal plasma membrane |
| GO:0005576 extracellular region | IEA GO_REF:0000044 | ACCEPT | Summary: Electronic mapping from the UniProt subcellular location "Secreted", which is itself experimentally supported by Mosquera et al. (2009). Reason: Correct mapping, consistent with the experimental annotation of BIC-directed secretion. Supporting Evidence: PMID:19357089 Therefore, BAS1 encodes a small unique protein that is secreted into BICs. |
| GO:0030430 host cell cytoplasm | EXP PMID:19357089 Interaction transcriptome analysis identifies Magnaporthe or... | ACCEPT | Summary: Mosquera et al. (2009) report that fluorescently labeled BAS proteins are secreted into rice cells and that BAS1 accumulates in BICs. In the full text, entry of BAS1 into the host cytoplasm is discussed as a possibility (BAS1 could be a structural BIC component or a translocated effector), with translocation cited as preliminary unpublished data; it was demonstrated directly in the follow-up study (Khang et al. 2010). Reason: The location is correct for BAS1 and is the core site of action of this cytoplasmic effector. The direct demonstration of translocation is in PMID:20435900 rather than this paper, which primarily documents BIC accumulation; the abstract statement that BAS proteins were secreted into rice cells supports the curator's reading, and the annotation is retained. Supporting Evidence: PMID:19357089 Fluorescently labeled BAS proteins were secreted into rice cells in distinct patterns in compatible, but not in incompatible, interactions. PMID:19357089 BAS1 and BAS2 might represent structural BIC components, or they might represent candidate effectors that are translocated across the EIHM into the rice cell. PMID:20435900 were translocated into the rice cytoplasm |
| GO:0030430 host cell cytoplasm | EXP PMID:20435900 Translocation of Magnaporthe oryzae effectors into rice cell... | ACCEPT | Summary: Khang et al. (2010) showed by live-cell imaging that BIC-localized BAS1 (like PWL2) is translocated into the cytoplasm of invaded rice cells and moves on into uninvaded neighbouring cells, whereas the interfacial protein BAS4 is not translocated. Translocation is blocked by clathrin-heavy-chain inhibitors (Oliveira-Garcia and Hamilton 2024). Reason: Direct experimental evidence; host cell cytoplasm is the core destination of this cytoplasmic effector. Supporting Evidence: PMID:20435900 were translocated into the rice cytoplasm PMID:20435900 and BAS1 proteins that reached the rice cytoplasm moved into uninvaded PMID:38722963 fluorescently labeled effectors Bas1 and Pwl2 in rice cells, leading to swollen |
| GO:0030430 host cell cytoplasm | IEA GO_REF:0000044 | ACCEPT | Summary: Electronic mapping from the UniProt subcellular location "Host cytoplasm", experimentally supported by Khang et al. (2010). Reason: Correct mapping, consistent with the experimental annotations. Supporting Evidence: PMID:20435900 were translocated into the rice cytoplasm |
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Download this section (compressed HTML)Q: What rice proteins does BAS1 bind once in the host cytoplasm, and does BAS1 alter host immunity or cellular processes? Reports that purified recombinant BAS1 induces callose and ROS while overexpression increases virulence (PMID:29551940) need independent confirmation with native-level expression.
Q: GO has no cellular component term for the biotrophic interfacial complex (BIC), a plant-derived interface structure that defines the cytoplasmic-effector class in M. oryzae. Should a host-cell interface term be requested so that BIC-localized effectors (BAS1, PWL2, AVR-Pita) can be distinguished from apoplastic effectors (BAS4, Slp1)?
Experiment: Identify host interactors of BAS1 by co-immunoprecipitation/mass spectrometry from infected rice tissue or yeast two-hybrid screening against an infected-sheath cDNA library, followed by in planta validation.
Experiment: Test bas1 deletion mutants in combination with other BIC effectors (to address redundancy), with complementation, using quantitative invasive-growth assays rather than lesion counts.
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