CASP-like protein 1D1 (CASPL1D1; At4g15610) is a four-transmembrane protein in the CASPL1 clade of the MARVEL-related CASP family. When expressed from the CASP1 promoter, it localizes to the lateral plasma membrane and is excluded from the Casparian strip membrane domain. In leaves, CASPL1D1 knockdown impairs pathogen-induced lignification and confinement of avirulent Pseudomonas syringae; combined disruption with CASPL4D1 increases these defects. A later native-promoter fusion study detected no endodermal expression under the conditions tested. The caspl1d1 caspl1d2 double mutant shows a small, condition-dependent enlargement of the continuous root suberization zone, without a detectable root hydraulic conductivity phenotype. CASPL1D1 has been reported among PIP2;1 interactors, but its individual biochemical function and contribution to the double-mutant phenotype remain unresolved.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005886 plasma membrane | IEA GO_REF:0000120 | ACCEPT | Summary: The electronic plasma-membrane assignment agrees with direct localization of ectopically expressed CASPL1D1. Reason: GO_REF:0000120 combines electronic annotation methods. UniProt cell-membrane localization is experimentally grounded in PMID:24920445, whose Figure 4A shows AtCASPL1D1 at the lateral plasma membrane, excluded from the Casparian strip domain. This supports the broad compartment without implying native endodermal expression. Supporting Evidence: file:ARATH/CASPL1D1/CASPL1D1-uniprot.txt SUBCELLULAR LOCATION: Cell membrane |
| GO:0003674 molecular_function | ND GO_REF:0000015 | ACCEPT | Summary: Retain the ND molecular-function root because a specific CASPL1D1 activity remains unestablished. Reason: GO_REF:0000015 documents the ND evidence convention, not an InterPro mapping. The reported PIP2;1 interaction and condition-dependent double-mutant suberization phenotype (PMID:30767240) do not establish a specific biochemical activity of CASPL1D1. Scaffold activity is a family-level hypothesis, and aquaporin regulation in that paper concerns CASPL1B1. The root records lack of characterized activity, not evidence that CASPL1D1 has no function. The OpenScientist hypothesis review agrees that membrane organization remains unresolved: PMID:31559647 provides CASPL1D1 knockdown evidence for immune lignification, but its tagged localization and complementation experiments use CASPL4D1. The CASP1-5 mechanism in PMID:36959183 likewise does not constitute an activity assay of CASPL1D1. |
| GO:0005794 Golgi apparatus | HDA PMID:22430844 Isolation and proteomic characterization of the Arabidopsis ... | UNDECIDED | Summary: Golgi purification identified a candidate proteome, but the At4g15610 enrichment and identification row remains unchecked. Reason: The Golgi purification study and its methods are accessible, but the At4g15610 identification and enrichment data in the supplementary protein table could not be inspected. Preserve the curator-supplied annotation pending the protein-level evidence; plasma-membrane localization does not contradict an endomembrane pool, and neither trafficking nor contamination has been demonstrated for CASPL1D1. |
| GO:0005794 Golgi apparatus | HDA PMID:25122472 Label-free protein quantification for plant Golgi protein lo... | UNDECIDED | Summary: The label-free Golgi assignment requires the unavailable At4g15610 row in Supplementary Table S4. Reason: The fractionation and label-free mass-spectrometry study is accessible, but the At4g15610 row in Supplementary Table S4 could not be retrieved. Preserve the curator-supplied annotation pending the protein-level evidence; plasma-membrane localization does not contradict an endomembrane pool, and neither trafficking nor contamination has been demonstrated for CASPL1D1. |
| GO:0005768 endosome | HDA PMID:22923678 Putative glycosyltransferases and other plant Golgi apparatu... | UNDECIDED | Summary: The LOPIT paper reports a combined Golgi/TGN class; a distinct endosome assignment for At4g15610 remains unverified. Reason: The accessible full text describes a combined Golgi/TGN classification, not independent resolution of all three GOA compartments; the At4g15610 assignment in Supplementary Table S2 could not be inspected. Preserve the curator-supplied annotation pending the protein-level evidence; plasma-membrane localization does not contradict an endomembrane pool, and neither trafficking nor contamination has been demonstrated for CASPL1D1. |
| GO:0005794 Golgi apparatus | HDA PMID:22923678 Putative glycosyltransferases and other plant Golgi apparatu... | UNDECIDED | Summary: The At4g15610 entry in the LOPIT Golgi/TGN classification table is needed to adjudicate this Golgi assignment. Reason: The accessible full text describes a combined Golgi/TGN classification, not independent resolution of all three GOA compartments; the At4g15610 assignment in Supplementary Table S2 could not be inspected. Preserve the curator-supplied annotation pending the protein-level evidence; plasma-membrane localization does not contradict an endomembrane pool, and neither trafficking nor contamination has been demonstrated for CASPL1D1. |
| GO:0005802 trans-Golgi network | HDA PMID:22923678 Putative glycosyltransferases and other plant Golgi apparatu... | UNDECIDED | Summary: LOPIT does not separately resolve Golgi and TGN in the main text, and the At4g15610 supplementary classification remains unchecked. Reason: The accessible full text describes a combined Golgi/TGN classification, not independent resolution of all three GOA compartments; the At4g15610 assignment in Supplementary Table S2 could not be inspected. Preserve the curator-supplied annotation pending the protein-level evidence; plasma-membrane localization does not contradict an endomembrane pool, and neither trafficking nor contamination has been demonstrated for CASPL1D1. |
| GO:0005886 plasma membrane | IDA PMID:24920445 Functional and Evolutionary Analysis of the CASPARIAN STRIP ... | ACCEPT | Summary: CASPL1D1 reaches the lateral plasma membrane under ectopic endodermal expression and is excluded from the Casparian strip domain. Reason: PMID:24920445 Figure 4A explicitly labels AtCASPL1D1 among the plasma-membrane proteins excluded from the CSD (asterisk); Figure 4B places it in the non-CSD group. The experiment used the CASP1 promoter, so it demonstrates subcellular targeting capacity rather than endogenous endodermal expression. PMID:36959183 subsequently detected no endodermal expression of its native-promoter fusion under the tested conditions. Supporting Evidence: PMID:24920445 AtCASPL1s excluded from the CSD but present at the lateral plasma membrane contain in the corresponding position an Ile (versus AtCASP1 Leu-140; one methyl group missing) and Tyr (versus AtCASP1 Phe-171; one extra hydroxyl group). PMID:36959183 However, expression analysis, using fluorescent CASPL fusion proteins in both wild-type and caspQ mutant background revealed either no endodermal expression (1D1) or an onset of expression too late to be responsible for the initiation of the lignin microdomains seen in caspQ mutants (Supplementary Fig. 3). |
| GO:0042742 defense response to bacterium | IMP PMID:31559647 Lignin-based barrier restricts pathogens to the infection si... | NEW | Summary: CASPL1D1 contributes to pathogen-induced lignified barriers that restrict avirulent Pseudomonas in leaves. Reason: PMID:31559647 Figure 5 shows that artificial-miRNA CASPL1D1 knockdown reduces induced lignification and permits greater bacterial growth and spread of hypersensitive cell death; combined CASPL4D1 disruption worsens the phenotype. This supports a defense process independently of the root double-mutant suberization observation. The evidence is knockdown rather than a clean null with complementation, and does not establish catalytic activity or the exact membrane-organizing mechanism. Independent OpenScientist adjudication supports this process-level conclusion. Figure 6 localization and complementation are CASPL4D1 experiments and are not counted as CASPL1D1 evidence. Increased spread of hypersensitive cell death is evidence for failed spatial containment, not direct execution of cell death. Supporting Evidence: PMID:31559647 AvrRpm1 ‐induced lignification was largely reduced in amiCASPL1D1 and caspl4d1 plants but was not affected in casp1‐1 and caspl5b3‐1 plants PMID:31559647 The restricted growth of Pst DC3000 ( AvrRpm1 ) and Pst DC3000 ( AvrRpt2 ) in wild‐type plants was alleviated in amiCASPL1D1 and caspl4d1 plants |
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Download this section (compressed HTML)Q: Does CASPL1D1 directly organize pathogen-induced membrane microdomains, or does its immune-barrier phenotype reflect trafficking or recruitment of another component?
Q: Which native cell types express CASPL1D1, and how does its individual loss contribute to the caspl1d1 caspl1d2 suberization phenotype?
Q: Do the proteomic endomembrane assignments represent stable localization, trafficking, or an unresolved fractionation signal?
Experiment: Compare caspl1d1, caspl1d2 and the double mutant with native-promoter complementation, measuring root suberization under control and NaCl conditions.
Hypothesis: CASPL1D1 makes a condition-dependent contribution to the double-mutant suberization phenotype.
Type: genetic complementation and root phenotyping
Experiment: Image a functional endogenous CASPL1D1 tag with plasma-membrane, Golgi and TGN markers across root cell types.
Hypothesis: Endogenous imaging can resolve the relationship between ectopic plasma-membrane targeting and proteomic endomembrane assignments.
Type: endogenous tagging and confocal colocalization
Experiment: Test independent CASPL1D1 null alleles with native-promoter complementation, alone and with caspl4d1, for infection-induced lignin distribution, bacterial spread and localized cell death. Use a rescue-competent CASPL1D1 tag to determine whether it accumulates at lignifying foci; imaging or complementation of CASPL4D1 cannot answer this question.
Hypothesis: CASPL1D1 itself contributes to immune-barrier organization, independently of artificial-miRNA off-target effects.
Type: genetics and infection-site imaging
Experiment: In a rescue-competent CASPL1D1-tagged line, measure membrane mobility and microdomain formation during infection, alongside recruitment of lignification machinery and secretory markers. Compare downstream machinery and secretory-marker distributions across wild type, CASPL1D1 loss and rescue without assuming the CASP1-5 exclusion mechanism is conserved.
Hypothesis: A direct membrane-organizing role predicts CASPL1D1-dependent microdomain behavior and spatial recruitment; a trafficking or accessory role may affect lignification without the same membrane organization.
Type: functional live-cell imaging and mobility measurements
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