PLP2 (patatin-like protein 2; also called pPLAIIalpha or AtPLA IIA; At2g26560) is a 407-residue soluble patatin-related phospholipase A of Arabidopsis thaliana. It has a PNPLA (patatin) domain with a GXSXG serine nucleophile (Ser66) and a DGA/G aspartate (Asp215) that form the patatin catalytic dyad, and it has no signal peptide. Purified recombinant PLP2 is a broad-specificity lipid acyl hydrolase. It releases fatty acids from both the sn-1 and sn-2 positions of phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, phosphatidic acid, phosphatidylserine and phosphatidylinositol. It also deacylates monogalactosyl- and digalactosyldiacylglycerol, including OPDA-containing arabidopsides, to the corresponding lyso-galactolipids. Knockout leaves contain less lysophosphatidylcholine and lysophosphatidylethanolamine, which shows that PLP2 hydrolyses membrane phospholipids in vivo. GFP fusions locate the protein to the cytoplasm. The gene is expressed mainly in roots and is strongly induced in leaves by pathogens and by abiotic stresses. Induction by Botrytis cinerea and avirulent Pseudomonas syringae depends on jasmonate and ethylene signalling. PLP2 promotes cell death: its level correlates with cell death after paraquat treatment or avirulent bacterial infection, and it strongly enhances lesion formation in the vad1 lesion-mimic mutant. As a result, PLP2 increases susceptibility to necrotrophic B. cinerea and weakens the hypersensitive-response restriction of avirulent P. syringae, but it contributes to resistance to Cucumber mosaic virus. PLP2 also affects oxylipin levels. Under basal conditions the knockout has more jasmonic acid, OPDA and 13-HPOT, whereas in Botrytis-challenged leaves alpha-dioxygenase-derived oxylipins accumulate in a PLP2-dependent manner. Knockout plants also lose water faster than wild type, through an ABA-independent mechanism.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004620 glycerophospholipase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference from PAINT node PTN001282408 (eukaryote-level, seeded by three Arabidopsis pPLAII paralogs). PLP2 lies inside this clade (PTHR32176:SF109), and its own purified recombinant protein hydrolyses all major glycerophospholipid classes at sn-1 and sn-2. Reason: This is the right level for PLP2's catalytic activity. Direct biochemistry on PLP2 (PMID:22259021) shows deacylation of PC, PE, PG, PA, PS and PI at both acyl positions, so a single positional term (phospholipase A1 or A2) would be too narrow. The deep IBD node placement agrees with the conserved Ser-Asp patatin dyad. Nothing suggests PLP2 has lost the ancestral activity. Supporting Evidence: PMID:22259021 Because the fluorescent label was at the sn -2 position, the detection of both the NBD-lysophospholipids and NBD-free fatty acid indicates that the enzyme releases fatty acids at both the sn -1 and sn -2 positions. PMID:22259021 Phospholipids are cleaved by pPLAIIΞ± at the sn -1 and sn -2 positions, and galactolipids, including those containing oxophytodienoic acids, can also serve as substrates. |
| GO:0005515 protein binding | IPI PMID:32612234 Extensive signal integration by the phytohormone protein net... | REMOVE | Summary: Yeast two-hybrid interaction with CYCB2-2 from the phytohormone protein network screen. Reason: Generic protein binding is uninformative under the protein-binding policy. No functional consequence of the PLP2-CYCB2-2 interaction has been reported, so no more specific molecular function can be inferred. Removing the term does not mean the interaction is false. Supporting Evidence: file:ARATH/PLP2/PLP2-uniprot.txt O48723; Q39070: CYCB2-2; NbExp=3; IntAct=EBI-4443426, EBI-2651372; |
| GO:0005515 protein binding | IPI PMID:32612234 Extensive signal integration by the phytohormone protein net... | REMOVE | Summary: Yeast two-hybrid interaction with the GRAS protein SCL23 from the phytohormone protein network screen. Reason: Generic protein binding is uninformative under the protein-binding policy. No functional consequence of the PLP2-SCL23 interaction has been reported. Removing the term does not mean the interaction is false. Supporting Evidence: file:ARATH/PLP2/PLP2-uniprot.txt O48723; Q9FHZ1: SCL23; NbExp=5; IntAct=EBI-4443426, EBI-1238460; |
| GO:0005737 cytoplasm | IDA PMID:16297072 A pathogen-inducible patatin-like lipid acyl hydrolase facil... | ACCEPT | Summary: PLP2-GFP fusion in Arabidopsis is cytoplasmic. An independent AtPLA IIA-GFP fusion transiently expressed in tobacco leaves is also cytoplasmic, not vacuolar. Reason: Two independent GFP studies agree, and the protein has no signal peptide or targeting sequence. The cytoplasm is where the soluble enzyme meets its membrane substrates. Supporting Evidence: PMID:16297072 PLP2 encodes a cytoplasmic lipid acyl hydrolase with wide substrate specificity PMID:12226489 For AtPLA IIA, AtPLA IVA, and AtPLA IVC, a cytoplasmic localization is suggested, but association with membranes (e.g. plasma membrane or ER) cannot be excluded. |
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping, based on the curated cytoplasm statement backed by PMID:12226489 and PMID:16297072. Reason: The electronic row matches the experimental cytoplasm localization. Supporting Evidence: PMID:12226489 For AtPLA IIA, AtPLA IVA, and AtPLA IVC, a cytoplasmic localization is suggested, but association with membranes (e.g. plasma membrane or ER) cannot be excluded. |
| GO:0005777 peroxisome | HDA PMID:28887381 Global Analysis of Membrane-associated Protein Oligomerizati... | UNDECIDED | Summary: High-throughput assignment from a leaf membrane-fraction SEC/LC-MS profiling study. The organelle call for PLP2 sits in supplemental tables that are not in the cached text. Reason: The study's own point is that many soluble proteins partition between cytosolic and membrane-associated pools. A peroxisomal call in fractionation data could therefore reflect membrane association or co-fractionation rather than residence in peroxisomes. PLP2 has no PTS1/PTS2 signal annotated, and no targeted study places it in peroxisomes. The specific assignment cannot be verified, so this row is left undecided rather than removed. Supporting Evidence: PMID:28887381 Over 150 proteins had a complicated localization pattern, and were clearly partitioned between cytosolic and membrane-associated pools. |
| GO:0006629 lipid metabolic process | IDA PMID:16297072 A pathogen-inducible patatin-like lipid acyl hydrolase facil... | MODIFY | Summary: Based on lipid acyl hydrolase activity of recombinant PLP2 and on lipid changes in transgenic plants. Reason: The term is correct but too general. PLP2 breaks down membrane glycerolipids. The knockout has less LPC and LPE (PMID:22259021), so PLP2 deacylates phospholipids in vivo. Phospholipid catabolic process is the precise term these data support. Galactolipid hydrolysis has been shown only in vitro, so galactolipid catabolic process is not proposed here. Proposed replacements: phospholipid catabolic process Supporting Evidence: PMID:22259021 pPLAIIΞ± KO leaves contained approximately 30 and 15% less LPC and LPE, respectively, but the level of LPG was the same in the KO and wild-type (WT) leaves PMID:16297072 PLP2 encodes a cytoplasmic lipid acyl hydrolase with wide substrate specificity |
| GO:0006629 lipid metabolic process | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping from the PNPLA domain (IPR002641). Reason: The PNPLA domain mapping is correct but general. Gene-specific evidence supports the more precise phospholipid catabolic process, as for the IDA row on the same term. Proposed replacements: phospholipid catabolic process Supporting Evidence: file:ARATH/PLP2/PLP2-uniprot.txt InterPro; IPR002641; PNPLA_dom. PMID:22259021 pPLAIIΞ± KO leaves contained approximately 30 and 15% less LPC and LPE, respectively |
| GO:0009507 chloroplast | ISM GO_REF:0000122 | REMOVE | Summary: AtSubP sequence-based localization prediction. Reason: Experimental evidence contradicts this prediction. AtPLA IIA (PLP2)-GFP is cytoplasmic in two independent studies (PMID:12226489, PMID:16297072). In the 2002 study only AtPLA I-GFP, a different gene, co-localized with chloroplasts. None of the Arabidopsis pPLAs has an N-terminal targeting peptide. Supporting Evidence: PMID:12226489 As demonstrated by a series of optical sections from palisade parenchyma cells and additional data (not shown), the hybrid protein At PLA I-GFP colocalized with chloroplasts PMID:12226489 For AtPLA IIA, AtPLA IVA, and AtPLA IVC, a cytoplasmic localization is suggested |
| GO:0009626 plant-type hypersensitive response | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: PAINT IBD at the Brassicaceae node PTN004927362, seeded by PLP2's own experimental annotation. Reason: PLP2 appearing in its own WITH/FROM is expected: its experimental HR data seeded the node. Biologically, PLP2 modulates HR-type cell death. It potentiates cell death after avirulent P. syringae infection while weakening bacterial restriction, and it contributes to HR-associated resistance to CMV. The plausible mechanism is lipolytic execution of cell death (see the programmed cell death row). The HR outcome is pathogen-dependent and a step removed from PLP2's catalytic role, so this term is kept as non-core. The PAINT curator limited the node to Brassicaceae (taxon:3700), not the deep pPLAII node, so the claim should not be transferred to grass paralogs. Supporting Evidence: PMID:16297072 PLP2 potentiates plant cell death inflicted by Botrytis and reduces the efficiency of the hypersensitive response in restricting the multiplication of avirulent bacteria PMID:19271961 PLP2 contributes to resistance to Cucumber mosaic virus, an obligate parasite inducing the hypersensitive response |
| GO:0009626 plant-type hypersensitive response | IEP PMID:16297072 A pathogen-inducible patatin-like lipid acyl hydrolase facil... | KEEP AS NON CORE | Summary: PLP2 protein accumulates in leaves challenged with avirulent P. syringae pv. tomato (avrRpt2), which triggers HR. Reason: Induction during HR is consistent with PLP2's modulatory role but is expression evidence only. The action matches the other HR rows. Supporting Evidence: PMID:16297072 accumulation of PLP2 protein in response to Botrytis cinerea or Pseudomonas syringae pv. tomato (avrRpt2) is dependent on jasmonic acid and ethylene signaling |
| GO:0009626 plant-type hypersensitive response | IMP PMID:16297072 A pathogen-inducible patatin-like lipid acyl hydrolase facil... | KEEP AS NON CORE | Summary: Silenced and overexpressing lines change cell death and bacterial restriction after avirulent P. syringae infection. Reason: The experimental evidence that PLP2 affects the HR is solid. It increases cell death and lowers the efficiency of bacterial restriction, so it is a modulator of the HR rather than a core component of the response. Kept as non-core for the same reasons as the IBA row. Supporting Evidence: PMID:16297072 We also established a positive correlation between the level of PLP2 expression in transgenic plants and cell death or damage in response to paraquat treatment or infection by avirulent P. syringae |
| GO:0012501 programmed cell death | IGI PMID:19271961 The Arabidopsis patatin-like protein 2 (PLP2) plays an essen... | ACCEPT | Summary: Genetic interaction with the lesion-mimic mutant vad1 (AT1G02120). PLP2 overexpression strongly promotes, and silencing reduces, necrotic lesions in vad1. PLP2 levels also correlate with cell death after paraquat or avirulent bacteria. Reason: PLP2 promotes cell death in several independent settings: genetically controlled (vad1), chemically induced (paraquat) and pathogen-induced. The authors describe it as "an integral component of the plant cell death execution machinery". PLP2 plausibly does part of the work: as a membrane-lipid acyl hydrolase it degrades membrane glycerolipids during cell death, rather than only signalling upstream. The full text is not cached, so the exact mechanism rests on the curators' reading and the authors' interpretation. Supporting Evidence: PMID:19271961 Phenotypic analysis of double-mutant progeny showed that PLP2 expression strongly promotes necrotic symptoms in vad1 leaves PMID:19271961 PLP2 is an integral component of the plant cell death execution machinery PMID:16297072 We also established a positive correlation between the level of PLP2 expression in transgenic plants and cell death or damage in response to paraquat treatment |
| GO:0016020 membrane | IDA PMID:16297072 A pathogen-inducible patatin-like lipid acyl hydrolase facil... | ACCEPT | Summary: Membrane association reported for PLP2 by the original characterisation study. The details are in the full text, which is not cached. Reason: A soluble patatin-type lipase acting on membrane glycerolipids is expected to associate peripherally with membranes. The independent GFP study explicitly leaves membrane association open, and a membrane-fraction proteome recovered PLP2. No more specific membrane is established, so the general term is as precise as the evidence allows. Accepted, deferring to the curator who read the full text. Supporting Evidence: PMID:12226489 For AtPLA IIA, AtPLA IVA, and AtPLA IVC, a cytoplasmic localization is suggested, but association with membranes (e.g. plasma membrane or ER) cannot be excluded. |
| GO:0016298 lipase activity | IDA PMID:16297072 A pathogen-inducible patatin-like lipid acyl hydrolase facil... | MODIFY | Summary: Recombinant PLP2 is a lipid acyl hydrolase with wide substrate specificity. Reason: The activity is real but the term is too general. Purified PLP2 deacylates glycerophospholipids at sn-1 and sn-2, and MGDG/DGDG to lyso-galactolipids (PMID:22259021). Glycerophospholipase activity, which PLP2 already carries by IBA, and galactolipase activity are the specific descendants these data support. Proposed replacements: glycerophospholipase activity galactolipase activity Supporting Evidence: PMID:16297072 PLP2 encodes a cytoplasmic lipid acyl hydrolase with wide substrate specificity PMID:22259021 pPLAIIΞ± also acted on nearly every species of MGDG and DGDG ( Figure 3A ), including those containing OPDA ( Figure 3B ), resulting in the production of corresponding lysogalactolipids monogalactosyl monoacylglyceride and digalactosyl monoacylglyceride |
| GO:0016298 lipase activity | IEA GO_REF:0000117 | MODIFY | Summary: ARBA machine-learning rule assigning lipase activity. Reason: The prediction is right but general. Direct biochemistry supports glycerophospholipase activity and galactolipase activity (PMID:22259021), as for the IDA row. Proposed replacements: glycerophospholipase activity galactolipase activity Supporting Evidence: PMID:22259021 Phospholipids are cleaved by pPLAIIΞ± at the sn -1 and sn -2 positions, and galactolipids, including those containing oxophytodienoic acids, can also serve as substrates. |
| GO:0031408 oxylipin biosynthetic process | IMP PMID:19271961 The Arabidopsis patatin-like protein 2 (PLP2) plays an essen... | KEEP AS NON CORE | Summary: In Botrytis-infected leaves, alpha-dioxygenase-pathway oxylipins accumulate in a PLP2-dependent manner. Reason: PLP2 affects oxylipin levels, but the sign depends on context. In infected leaves some alpha-DOX products depend on PLP2 (PMID:19271961), consistent with PLP2 releasing fatty-acid precursors, which would be participation in the first step. In unchallenged leaves the knockout has more JA, MeJA, OPDA and 13-HPOT (PMID:22259021), and those authors conclude that PLP2 negatively regulates oxylipin production. Because the role differs by condition and the precursor-supply mechanism has not been shown directly, the term is kept as non-core. Supporting Evidence: PMID:19271961 Several compounds previously described as modulating plant tissue damage and issued from the alpha-dioxygenase pathway were found to accumulate in a PLP2-dependent manner PMID:22259021 These results indicate that pPLAIIΞ± negatively regulates oxylipin production and suggest a role in the removal of oxidatively modified fatty acids from membranes. |
| GO:0042802 identical protein binding | IPI PMID:21798944 Evidence for network evolution in an Arabidopsis interactome... | KEEP AS NON CORE | Summary: PLP2 self-interaction detected in the Arabidopsis Interactome-1 Y2H map. Reason: The self-interaction has been reproduced in two Y2H screens. Its significance for activity is unknown: patatin oligomerization has not been shown to matter for PLP2 function. Kept as non-core. Supporting Evidence: file:ARATH/PLP2/PLP2-uniprot.txt O48723; O48723: PLP2; NbExp=4; IntAct=EBI-4443426, EBI-4443426; |
| GO:0042802 identical protein binding | IPI PMID:32612234 Extensive signal integration by the phytohormone protein net... | KEEP AS NON CORE | Summary: PLP2 self-interaction detected again in the phytohormone protein network Y2H screen. Reason: Independent replication of the Y2H self-interaction. Non-core, as for the row above. Supporting Evidence: file:ARATH/PLP2/PLP2-uniprot.txt O48723; O48723: PLP2; NbExp=4; IntAct=EBI-4443426, EBI-4443426; |
| GO:0046686 response to cadmium ion | IEP PMID:17075075 Proteome changes in Arabidopsis thaliana roots upon exposure... | KEEP AS NON CORE | Summary: Root proteome change after 24 h of 10 uM Cd2+. The cached abstract does not name PLP2, which presumably appears in the full-text spot list. Reason: This is expression-level evidence only, in a tissue (root) where PLP2 is mainly expressed. It fits the gene's broad stress inducibility (PMID:14634163) and says nothing about the protein's activity. Kept as non-core, deferring to the curator on the identification. Supporting Evidence: PMID:17075075 Alterations in the root proteome of hydroponically grown Arabidopsis thaliana plants treated with 10 microM Cd(2+) for 24 h are reported here. PMID:14634163 Expression of Arabidopsis phospholipase A IIA (AtPLA IIA) gene was induced by various treatments |
| GO:0047372 monoacylglycerol lipase activity | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: PAINT IBD at the eukaryote-level node PTN001282408, seeded by the pPLAII paralogs AT4G37050/AT4G37060/AT4G37070. Reason: PLP2 is inside the clade that carries this IBD and keeps the catalytic dyad, so inheriting the activity is plausible. Monoacylglycerol hydrolysis has not been tested for PLP2 itself. The published PLP2 assays used diacyl phospholipids and galactolipids (PMID:22259021). The term is kept as a peripheral, phylogenetically inferred activity, not part of the experimentally established core. Supporting Evidence: PMID:22259021 The serine and aspartic acid residues constitute a catalytic dyad for its acyl hydrolase activity |
| GO:0051607 defense response to virus | IMP PMID:19271961 The Arabidopsis patatin-like protein 2 (PLP2) plays an essen... | KEEP AS NON CORE | Summary: PLP2-silenced and overexpressing plants show that PLP2 contributes to resistance to Cucumber mosaic virus, which induces an HR. Reason: This is an organismal resistance phenotype. PLP2 most likely contributes through its general promotion of HR-associated cell death, not through any antiviral activity of its own. Kept as non-core, deferring to the curator's full-text reading. Supporting Evidence: PMID:19271961 PLP2 contributes to resistance to Cucumber mosaic virus, an obligate parasite inducing the hypersensitive response |
| GO:0071456 cellular response to hypoxia | IEP PMID:21398256 The AP2/ERF transcription factor AtERF73/HRE1 modulates ethy... | KEEP AS NON CORE | Summary: Expression change under hypoxia in a study of AtERF73/HRE1. PLP2 is not named in the cached abstract. Reason: Expression-only evidence, consistent with PLP2's ethylene inducibility. It does not establish a role in the hypoxia response. Kept as non-core, deferring to the curator on the full text. Supporting Evidence: PMID:21398256 hypoxia-inducible genes could be affected by AtERF73/HRE1-RNAi lines in two different ways |
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Download this section (compressed HTML)Q: Which membrane lipid species does PLP2 hydrolyse in vivo during cell death, and does its lipolytic activity drive membrane breakdown directly or by supplying fatty-acid precursors for alpha-dioxygenase-derived oxylipins?
Q: How can loss of PLP2 raise basal JA and OPDA (PMID:22259021) while PLP2 is required for alpha-DOX oxylipin accumulation in Botrytis-infected leaves (PMID:19271961)? Is the preference for oxidised acyl chains condition-dependent?
Q: Do the grass pPLAII-like paralogs (PTHR32176 SF103/SF26) keep PLP2's broad sn-1/sn-2 and galactolipid specificity, given that they are out-paralogs separated at duplication node PTN009133995?
Experiment: Make a catalytically dead PLP2 (S66A or D215N) and test whether it complements the knockout or overexpression phenotypes: vad1 lesion enhancement, paraquat cell death, Botrytis susceptibility and leaf water loss. This would show whether the cell-death role needs acyl hydrolase activity.
Experiment: Run lipidomics on oxidised and unoxidised membrane lipids in plp2 knockout and catalytic-mutant lines during Botrytis infection and vad1 lesion formation, to identify the in vivo substrates.
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