Confirms that UniProt P25317 corresponds to tobacco parA, which is sequence-identical to the defense gene str246C, and maps parA to the auxin-regulated tobacco type-III (tau-class) GST subfamily Nt114 (older nomenclature GST3-1).

The "auxin-regulated" designation reflects transcriptional induction: the str246C/parA promoter is induced by auxin (2,4-D) via a defined auxin-responsive cis-element, and is independently a multi-stimulus response promoter activated by wounding (within 30 min), elicitors and bacterial infection - supporting the conclusion that parA is a downstream auxin/stress-responsive target gene, not a component of the auxin signal-transduction pathway.

Direct GST enzymology in the retrieved corpus is demonstrated for the paralogs parB and the Nt103/Nt107 isozymes (GST1-1/GST2-1), not for parA itself; parA-specific catalytic activity is weak, so EC 2.5.1.18 / GST activity for P25317 is best annotated as "probable" on the basis of family placement plus weak directly-detected activity.

Subcellular localization of parA remains unsettled: a protoplast immunostaining study reported nuclear localization, while BY-2 proteomics detected P25317 in plastid preparations and whole-cell 2-DE; the plastid-fraction detection may reflect contamination, so neither cytoplasm nor nucleus can be asserted with confidence.

A 2024 synthesis on plant GSTs (Micic et al.) notes that GST substrate promiscuity and the difficulty of detecting endogenous glutathione conjugates mean the physiological substrate of a probable GST such as parA cannot be assigned from sequence similarity alone.

SwissProt keyword-derived (SPKW) annotations present in the Sept 2025 goa_uniprot_gcrp snapshot but removed from the current GOA release after GOA retired the keyword2GO pipeline for cellular organisms.

The SPKW annotation auxin-activated signaling pathway (GO:0009734) for parA was derived from the UniProt keyword "Auxin signaling pathway", itself based on the historical protein name "Auxin-regulated protein"; it conflates auxin-responsiveness with auxin-pathway-component status and its removal was justified.

Cytoplasm localization was transferred from the PTHR11260 GST family; this is the family-typical location for cytosolic plant GSTs.

Glutathione transferase activity and glutathione metabolic process were inferred from the InterPro tau-class GST signature (IPR045074), the RHEA reaction RHEA:16437, EC 2.5.1.18 and PANTHER family membership.

parA (par) was isolated as an auxin-regulated cDNA from cultured tobacco mesophyll protoplasts; its 220-aa product had no detectable homology to known proteins at the time of isolation.

par mRNA accumulates within 30 min of 2,4-D addition and is absent in leaves, freshly prepared protoplasts, or protoplasts without auxin, establishing parA as a rapidly auxin-induced gene.

A 111-bp direct repeat in the parA promoter constitutes an auxin-responsive cis-element required for auxin-mediated transcriptional activation.

The genomic gene str246C is sequence-identical to parA.

str246C/parA transcripts accumulate in tobacco leaves on inoculation with the bacterial pathogen Pseudomonas (Ralstonia) solanacearum, in both compatible and incompatible interactions, identifying parA as a defense/stress-responsive gene.

parB (Nt103), a close paralog of parA isolated from the same auxin-induced tobacco protoplast system, has clear sequence homology to glutathione S-transferases (EC 2.5.1.18).

Recombinant parB expressed in E. coli has GST activity, and GST activity increases in tobacco protoplasts cultured with 2,4-D, directly linking the par GST family to auxin-induced glutathione transferase function.

The parA recombinant protein has only a low level of GST activity, below 1/30 that of the parB GST.

Immunofluorescence and confocal microscopy localized parA protein to the nucleus (excluded from the nucleolus) of tobacco protoplasts and BY-2 cells, in contrast to conventional cytoplasmic GSTs such as parB.

The authors proposed that parA may have a function distinct from a conventional cytosolic GST, possibly related to transcription, although this remains speculative and based on a weak similarity to an E. coli RNA-polymerase-binding protein.

The plant-specific phi (F) and tau (U) GST classes catalyse glutathione-dependent conjugation of xenobiotics, leading to detoxification; plant GSTs use a catalytic serine rather than the tyrosine of mammalian GSTs.

Endogenous roles of plant GSTs are less well defined and include signaling, counteracting oxidative stress, and transport of secondary metabolites.

Soluble plant GSTs (EC 2.5.1.18) form a large gene family divided into phi, tau, theta, zeta and lambda classes; tau and phi are plant-specific and the most numerous.

Plant GSTs are predominantly cytosolic and use glutathione as a cosubstrate or coenzyme for conjugation, peroxide reduction, isomerization and non-catalytic ligandin functions.