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An Arabidopsis quiescin-sulfhydryl oxidase regulates cation homeostasis at the root symplast-xylem interface.

ABSTRACT: A genetic screen of Arabidopsis 'activation-tagging' mutant collection based on tolerance to norspermidine resulted in a dominant mutant (par1-1D) with increased expression of the QSO2 gene (At1g15020), encoding a member of the quiescin-sulfhydryl oxidase (QSO) family. The par1-1D mutant and transgenic plants overexpressing QSO2 cDNA grow better than wild-type Arabidopsis in media with toxic cations (polyamines, Li(+) and Na(+)) or reduced K(+) concentrations. This correlates with a decrease in the accumulation of toxic cations and an increase in the accumulation of K(+) in xylem sap and shoots. Conversely, three independent loss-of-function mutants of QSO2 exhibit phenotypes opposite to those of par1-1D. QSO2 is mostly expressed in roots and is upregulated by K(+) starvation. A QSO2Colon, two colonsGFP fusion ectopically expressed in leaf epidermis localized at the cell wall. The recombinant QSO2 protein, produced in yeast in secreted form, exhibits disulfhydryl oxidase activity. A plausible mechanism of QSO2 action consists on the activation of root systems loading K(+) into xylem, but different from the SKOR channel, which is not required for QSO2 action. These results uncover QSOs as novel regulators of ion homeostasis.

SUBMITTER: Alejandro S

PROVIDER: S-EPMC1914105 | biostudies-literature | 2007 Jul

REPOSITORIES: biostudies-literature

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An Arabidopsis quiescin-sulfhydryl oxidase regulates cation homeostasis at the root symplast-xylem interface.

Alejandro Santiago S Rodríguez Pedro L PL Bellés Jose M JM Yenush Lynne L García-Sanchez María J MJ Fernández José A JA Serrano Ramón R

The EMBO journal 20070614 13

A genetic screen of Arabidopsis 'activation-tagging' mutant collection based on tolerance to norspermidine resulted in a dominant mutant (par1-1D) with increased expression of the QSO2 gene (At1g15020), encoding a member of the quiescin-sulfhydryl oxidase (QSO) family. The par1-1D mutant and transgenic plants overexpressing QSO2 cDNA grow better than wild-type Arabidopsis in media with toxic cations (polyamines, Li(+) and Na(+)) or reduced K(+) concentrations. This correlates with a decrease in ...[more]

PMID: 17568770

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Project description:BackgroundThe enzyme family Quiescin Sulfhydryl Oxidase (QSOX) is defined by the presence of an amino-terminal thioredoxin-fold (Trx) domain and a carboxy-terminal Erv family sulfhydryl oxidase domain. QSOX enzymes, which generate disulfide bonds and transfer them to substrate proteins, are present in a wide variety of eukaryotic species including metazoans and plants, but are absent from fungi. Plant and animal QSOXs differ in their active-site amino acid sequences and content of non-catalytic domains. The question arises, therefore, whether the Trx-Erv fusion has the same mechanistic significance in all QSOX enzymes, and whether shared features distinguish the functional domains of QSOX from other instances in which these domains occur independently. Through a study of QSOX phylogeny and an analysis of QSOX sequence diversity in light of recently determined three-dimensional structures, we sought insight into the origin and evolution of this multi-domain redox alliance.ResultsAn updated collection of QSOX enzymes was used to confirm and refine the differences in domain composition and active-site sequence motif patterns of QSOXs belonging to various eukaryotic phyla. Beyond the expected phylogenetic distinction of animal and plant QSOX enzymes, trees based on individual redox-active QSOX domains show a particular distinction of the Trx domain early in plant evolution. A comparison of QSOX domains with Trx and Erv domains from outside the QSOX family revealed several sequence and structural features that clearly differentiate QSOXs from other enzymes containing either of these domains. Notably, these features, present in QSOXs of various phyla, localize to the interface between the Trx and Erv domains observed in structures of QSOX that model interdomain redox communication.ConclusionsThe infrastructure for interdomain electron relay, previously identified for animal and parasite QSOXs, is found broadly across the QSOX family, including the plant enzymes. We conclude that the conserved three-dimensional framework of the QSOX catalytic domains accommodates lineage-specific differences and paralog diversification in the amino acid residues surrounding the redox-active cysteines. Our findings indicate that QSOX enzymes are characterized not just by the presence of the two defining domain folds but also by features that promote coordinated activity.

Dataset Information

An Arabidopsis quiescin-sulfhydryl oxidase regulates cation homeostasis at the root symplast-xylem interface.

Publications

An Arabidopsis quiescin-sulfhydryl oxidase regulates cation homeostasis at the root symplast-xylem interface.

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