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 ... | KEEP AS NON CORE | Summary: Parsons et al. (2012) purified Arabidopsis Golgi membranes by density centrifugation and free-flow electrophoresis and defined a reproducible Golgi proteome. TAIR's HDA row records CASPL1D1 (At4g15610) in that dataset. Reason: The At4g15610 entry is in the supplementary table, which could not be retrieved. The HDA row itself records that the curators found it there, and nothing contradicts the identification. Three independent Golgi proteomics methods from this paper, PMID:25122472 and PMID:22923678 (purification by surface charge, label-free gradient profiling, and LOPIT isotope tagging) all place CASPL1D1 in the Golgi. That convergence makes a Golgi pool credible. For a multi-pass plasma-membrane protein, a Golgi pool is expected during biosynthetic transit, and the LOPIT authors note that the Golgi contains proteins en route to other organelles. The steady-state functional location established by imaging is the plasma membrane (PMID:24920445), so the Golgi location is retained as non-core. Supporting Evidence: PMID:22430844 A collection of 371 proteins consistently identified in all replicates has been proposed to represent the Golgi proteome, marking an appreciable advancement in numbers of Golgi-localized proteins. PMID:22923678 Furthermore, the Golgi apparatus contains proteins en route to other organelles because of anterograde and retrograde trafficking in the endomembrane system. PMID:24920445 AtCASPL1s excluded from the CSD but present at the lateral plasma membrane |
| GO:0005794 Golgi apparatus | HDA PMID:25122472 Label-free protein quantification for plant Golgi protein lo... | KEEP AS NON CORE | Summary: Nikolovski et al. (2014) combined Golgi-targeted density-gradient fractionation with label-free quantitative MS to localize and quantify Golgi proteins. TAIR's HDA row records CASPL1D1 among the Golgi-assigned proteins. Reason: The At4g15610 row in the supplementary table could not be retrieved, but the HDA annotation records the curators' reading of it and nothing contradicts it. This is an independent method (gradient-profile classification) that agrees with the purified-Golgi (PMID:22430844) and LOPIT (PMID:22923678) assignments. A Golgi pool of this plasma-membrane CASP-like protein is therefore credible, most simply as secretory transit, and it is retained as non-core relative to the imaging-established plasma-membrane location. Supporting Evidence: PMID:25122472 The method was also able to classify proteins as Golgi localized based on their subcellular fractionation profile. PMID:22923678 Furthermore, the Golgi apparatus contains proteins en route to other organelles because of anterograde and retrograde trafficking in the endomembrane system. |
| GO:0005768 endosome | HDA PMID:22923678 Putative glycosyltransferases and other plant Golgi apparatu... | KEEP AS NON CORE | Summary: The LOPIT study (Nikolovski et al. 2012) classified 197 previously unlocalized proteins into a combined Golgi/TGN class. GOA represents that class as Golgi apparatus, trans-Golgi network and endosome rows for CASPL1D1. Reason: LOPIT did not resolve endosomes as a separate class, so this row reflects the combined Golgi/TGN assignment. In plants the trans-Golgi network acts as the early endosome, so an endosome annotation follows from a Golgi/TGN assignment and is not contradicted by it. The exact At4g15610 supplementary row could not be inspected, but the curated HDA rows record its classification. Endosome is retained as a non-core endomembrane location, consistent with the Golgi and TGN rows from the same dataset. The steady-state functional site is the plasma membrane. Supporting Evidence: PMID:22923678 The application of the classification procedure to the proteins with unknown localization resulted in a list of 197 proteins classified as Golgi/ TGN localized ( Supplemental Table S2 ). |
| GO:0005794 Golgi apparatus | HDA PMID:22923678 Putative glycosyltransferases and other plant Golgi apparatu... | KEEP AS NON CORE | Summary: LOPIT isotope-tagging proteomics classified CASPL1D1 into the combined Golgi/TGN class. This independently agrees with the purified-Golgi and label-free fractionation datasets. Reason: This is a third, methodologically independent proteomic assignment of At4g15610 to the Golgi. It is consistent with the other Golgi rows, which are kept as non-core. The supplementary row was not retrievable, but the curated HDA annotation records it and nothing contradicts it. The authors note that the Golgi contains proteins in transit, which fits a plasma-membrane protein passing through the secretory pathway. Kept as non-core because the functional location is the plasma membrane (PMID:24920445). Supporting Evidence: PMID:22923678 The application of the classification procedure to the proteins with unknown localization resulted in a list of 197 proteins classified as Golgi/ TGN localized ( Supplemental Table S2 ). PMID:22923678 Furthermore, the Golgi apparatus contains proteins en route to other organelles because of anterograde and retrograde trafficking in the endomembrane system. |
| GO:0005802 trans-Golgi network | HDA PMID:22923678 Putative glycosyltransferases and other plant Golgi apparatu... | KEEP AS NON CORE | Summary: LOPIT placed CASPL1D1 in the combined Golgi/TGN class, which GOA represents in part as the trans-Golgi network. Reason: The LOPIT classifier assigns proteins to a joint Golgi/TGN class, so the TGN row is a faithful rendering of that classification, even though it does not discriminate TGN from Golgi cisternae. The TGN is the sorting station for plasma-membrane cargo in plants, so detection there fits secretory transit of this plasma-membrane protein. The supplementary row was not retrievable, but nothing contradicts the curated classification. Kept as non-core, consistent with the Golgi rows. Supporting Evidence: PMID:22923678 The application of the classification procedure to the proteins with unknown localization resulted in a list of 197 proteins classified as Golgi/ TGN localized ( Supplemental Table S2 ). |
| 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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