Table 1.
Pd-associated proteins (PdAPs) involved in regulation of Pd permeability.
| Protein | Function/Description | Signal Sequence | Predicted N-Glycosylation Sites | Pd Localization | Protein Relocation After Stress Impact | References |
|---|---|---|---|---|---|---|
| Pd non-secretory proteins | ||||||
| Actin, myosin and tubulin | Actin-myosin filaments and tubulin are localized within the Pd cytoplasmic sleeve and negatively control Pd permeability | No | No | Cytoplasmic sleeves in the Pd cavity | No | [48,49,50] |
| A. thaliana calreticulin-1 (AtCRT1) (UniProt O04151) | Ca2+-sequestering protein chaperone and ER protein that negatively control Pd permeability | Yes | Asn59, Asn154, Asn399 | Associates with the desmotubule | Yes | [51,52,53] |
| Tobacco non-cell autonomous pathway protein (NCAPP) (UniProt Q947H5) | NCAPP has homology to aldose 1-epimerase; positively controls Pd permeability and PME/methanol production | Yes | Asn76 and Asn100 | Localizes in the ER | N/A | [54,55] |
| Remorin | Associates with PM raft-like structures and probably serves as a negative regulator of Pd permeability. Antagonist of Potato virus X triple gene block protein 1 | No | No | In the cytosolic surface of the Pd plasma membrane | N/A | [56] |
| A. thaliana reticulons, AtRTNLB3 (UniProt Q9SH59) and AtRTNLB6 (UniProt Q6DBN4) | ER-localized proteins with three TM domains that negatively control Pd permeability | No | No | Accumulates in the desmotubule | N/A | [57,58] |
| Arabidopsis synaptotagmin SYTA (AtSYTA) (UniProt - Q9SKR2) | ER-PM tethering and endocytic recycling | No | No | Interacts with TMV movement protein (MP) Pd localization signal (PLS) for cell-to-cell transport and participates in the formation of virus replication sites | Suggested that SYTA relocates to the Pd cavity after TMV infection | [59,60,61,62] |
| Pd secretory proteins | ||||||
| A. thaliana (1,3)-β-glucanase 1 (AtBG1) (UniProt - Q9M2M0) | Callose-degrading enzymes that positively control Pd permeability | Yes | Asn291 | Colocalizes with callose near Pd orifices | No | [36,63,64] |
| A. thaliana (1,3)-β-glucanase 2 (AtBG2) (UniProt P33157) | Yes | No | Colocalizes with callose near Pd orifices in the extracellular space | AtBG2 is not delivered to the extracellular space in TMV-infected cells, but associates with viral MP in Pd cytoplasmic sleeve | [36,64] | |
|
A. thaliana (1,3)-β-glucanase 3 (AtBG3) (UniProt F4j270) |
Yes | No | Constitutive Pd-associated enzyme but not stress-regulated | No | [36,64] | |
| *A. thaliana β-1,3-glucanase_putative Pd-associated protein (AtBG_ppap) (UniProt Q9FHX5) | Yes | No | Localizes to the Pd neck region | No | [35,36,65] | |
| A. thaliana Class 1 reversibly glycosylated polypeptide (AtC1RGP) (UniProt Q9SRT9) | AtC1RGP acts as a negative Pd regulator. Despite having no signal sequence, it is found in the GA and ultimately in the Pd | No | No | N/A | [66,67,68] | |
| A. thaliana Callose synthase (CalS) (UniProt Q9AUE0) | Callose-synthesizing enzyme encoded by glucan synthase-like (GSL) gene that negatively controls Pd permeability | No (needs exocyst-positive organelle (EXPO)-mediated secretion for Pd localization) |
No | CalS localizes at callose depositions | No | [36,37,69] |
|
A. thaliana formin-like protein 1 (UniProt Q9SE97) and 2 (UniProt O22824) (AtFH1 and AtFH2) |
Negatively regulates Pd permeability by interacting with actin filaments | Yes | Multiple Asn sites | Localizes in the Pd cavity and interacts with actin | N/A | [70,71] |
| A. thaliana β-1,6-N-acetylglucosaminyl transferase-like enzyme (GnTL) (UniProt Q9SUZ8) | Interacts with calreticulin and probably serves as a negative regulator of Pd permeability | Yes | Asn287 and Asn316 | Colocalizes with callose-binding protein near Pd orifices | N/A | [72] |
| *A. thaliana Pd callose-binding proteins 1,2 and 3 (PDCB1-3) (At5g61130) |
Pd callose-binding protein that negatively controls Pd permeability | Yes | Asn154 and Asn179 | Localizes to the Pd neck | No | [73,74] |
|
A. thaliana Pd-located protein 1 (PDLP1) (UniProt Q8GXV7) |
Membrane receptor-like protein with two extracellular DUF26 domains. PDLP1 overexpression causes restricted cell-to-cell trafficking. Acts as a negative Pd regulator by promoting callose deposition. Stimulates the transport of viruses that use tubule-guided movement by redundantly interacting with tubule-forming MPs within Pds | Yes | No | PDLP1 is targeted to Pd via the Brefeldin A–sensitive secretory pathway and resides at Pd with its C-terminus in the cytoplasmic space and its N-terminus in the apoplast. | No | [75,76,77,78] |
|
A. thaliana Pd located protein 5 (PDLP5) (UniProt Q8GUJ2) |
A member of the PDLP family that has 30% amino acid sequence identity to PDLP1. Contains sphingolipid binding motif in the TMD. Acts as a negative Pd regulator by promoting callose deposition. Delays systemic movement of TMV | Yes | Asn69 and Asn132 | PDLP5 localizes inside the central Pd region similar to TMV MP. However, PDLP5/MP overlap is not complete | Transmembrane secretory protein with ectopic localization | [79,80,81,82] |
| Tobacco pectin methylesterase (PME) (UniProt Q9LEBO) |
Non-direct regulator of Pd permeability that participates in the de-methylesterification of cell wall HG through the formation of methanol | Yes | Asn43, Asn101 and Asn220 in proPME | Immunogold localization of PME is preferentially around Pd | No | [83,84] |
* glycosylphosphatidylinositol-anchored protein (GPI-AP) [85].