PINA is a canonical long-loop PIN auxin exporter in the moss Physcomitrium patens (historically Physcomitrella patens). It localizes at the plasma membrane, with polar enrichment at protonemal tips and context-dependent distribution in leaves. Native mutant combinations with PINB affect auxin distribution, gametophore leaf development and shoot tropisms. Radioactive auxin-export assays with induced PINA-GFP in moss support its exporter activity. PINA contributes more strongly than PINB to some auxin-sensitive gametophore phenotypes, while their reproductive contributions differ. During early leaf-like organ (phyllid) growth, PINA and PINB mainly regulate intracellular auxin levels; basal polarity appears only later in differentiated tip cells, so export does not imply directional transport at every developmental stage.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005783 endoplasmic reticulum | IBA GO_REF:0000033 | UNDECIDED | Summary: Native ER localization remains unresolved in its assay context. Reason: The ER IBD at PTN001589272 is a land-plant ancestral judgment seeded by Arabidopsis PIN5/6/8. Native moss PM localization does not exclude ER residence. The full 2014 study (PMID:25448003) explicitly discusses an earlier heterologous tobacco-protoplast PINA ER observation and reports non-colocalization of native PIN signal with the ER marker BIP2; the latter antibody experiment is not uniquely PINA-specific. These assay contexts do not settle native PINA ER residence. No target-specific loss or erroneous ancestral placement is established. Keep the root-organelle claim unresolved, without replacement by plasma membrane. Normal retrieval of the historical PMID:19506555 is abstract-only; the target-specific construct interpretation is available in the later full study, not independently re-established from the old abstract. Propagation Review Root cause: UNRESOLVED Sources checked: PANTHER:PTN001589272 UNRESOLVED ER source node and Arabidopsis PIN5/6/8 descendants inspected; native target ER residence is not resolved by PM localization. Supporting Evidence: PMID:37528584 PpPINA-GFP localized at the PM of the protonema tip with a clear polarity in both initial and elongated protonemata (Figure 4A). PMID:25448003 Our results suggest that PINA and PINB act redundantly to remove auxin from the apex and initiating leaves, allowing normal development to proceed. |
| GO:0005886 plasma membrane | IBA GO_REF:0000033 | ACCEPT | Summary: Native moss PIN reaches the plasma membrane. Reason: PMID:37528584 examines the target GFP fusion under its native promoter in moss. PINA is polar at filament tips, basal/apical in young leaves, and more even near leaf bases. This independently supports the PAINT localization. The 2026 native phyllid time series (PMID:41984944) independently confirms membrane localization while restricting basal polarity to later differentiated tip cells, not early growing phyllids. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN001589272 SUPPORTS TRANSFER Native target GFP localization supports inheritance of PM localization. Supporting Evidence: PMID:37528584 PpPINA-GFP localized at the PM of the protonema tip with a clear polarity in both initial and elongated protonemata (Figure 4A). PMID:41984944 both PINA-GFP and PINB-GFP signals were primarily detected at membranes, without any clear basal polarization |
| GO:0016020 membrane | IEA GO_REF:0000120 | MODIFY | Summary: Membrane localization can be refined to plasma membrane. Reason: Native target localization supports the more precise GO:0005886, already represented in this review. This is refinement of generic membrane and does not remove a potentially separate ER pool. The 2026 native phyllid time series (PMID:41984944) independently confirms membrane localization while restricting basal polarity to later differentiated tip cells, not early growing phyllids. Proposed replacements: plasma membrane Supporting Evidence: PMID:37528584 PpPINA-GFP localized at the PM of the protonema tip with a clear polarity in both initial and elongated protonemata (Figure 4A). PMID:41984944 both PINA-GFP and PINB-GFP signals were primarily detected at membranes, without any clear basal polarization |
| GO:0022857 transmembrane transporter activity | IBA GO_REF:0000033 | MODIFY | Summary: The transporter activity is specifically auxin efflux. Reason: The general PAINT transporter function is correct and can be made substrate- and direction-specific. PMID:37528584 directly measures increased H3-IAA release from induced PINA-GFP moss lines. Refine to GO:0010329; native developmental phenotypes alone are not a direct turnover measurement. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN002065923 SUPPORTS TRANSFER The inspected PAINT node supports general transmembrane transport from Arabidopsis PIN descendant evidence; independent moss experiments justify substrate/direction refinement without rejecting ancestral transporter function. Proposed replacements: auxin efflux transmembrane transporter activity Supporting Evidence: PMID:37528584 In comparison with the WT, all examined PIN-GFP plants showed a higher amount of radioactive auxin in the culture medium, indicating their auxin export activity (Figure 3B). PMID:37528584 We determined the localization pattern of the PIN proteins by fusing GFP to AtPIN1, AtPIN2, PpPINA, and MpPINZ as shown in Figure 3A (Zhang et al., 2019). |
| GO:0055085 transmembrane transport | IEA GO_REF:0000002 | MODIFY | Summary: Transmembrane transport is specifically auxin export. Reason: The PIN protein performs auxin export, so the generic BP can be refined to GO:0010315. The induced PINA-GFP assay measures release into moss culture medium (PMID:37528584). Cell-to-environment export is not by itself proof of tissue-scale canalization, nor does it establish universal ABCB/AGC-kinase dependence. The 2026 phyllid study supports export-mediated control of intracellular auxin rather than early basipetal tissue transport; it does not negate exporter activity. Proposed replacements: auxin export across the plasma membrane Supporting Evidence: PMID:37528584 In comparison with the WT, all examined PIN-GFP plants showed a higher amount of radioactive auxin in the culture medium, indicating their auxin export activity (Figure 3B). PMID:37528584 We determined the localization pattern of the PIN proteins by fusing GFP to AtPIN1, AtPIN2, PpPINA, and MpPINZ as shown in Figure 3A (Zhang et al., 2019). |
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