Functions of PSK-a and analysis of the PSK-signaling pathway in Arabidopsis thaliana

Phytosulfokin-a (PSK-a) ist ein disulfatiertes Pentapeptid mit der Aminosäuresequenz Tyr(SO3H)-Ile-Tyr(SO3H)-Thr-Gln, welches als autokriner Wachstumsfaktor wirkt. Über physiologische und molekulargenetische Ansätze wurden in Arabidopsis thaliana Funktionen von PSK-a und eine mögliche Komponente des Signalweges identifiziert. PSK-Präproproteine werden in Arabidopsis durch fünf Gene kodiert. Die Perzeption des Peptids erfolgt in Arabidopsis durch zwei Rezeptorkinasen mit Leuzinreichen Wiederholungssequenzen, PSKR1 und PSKR2. Spezifische Expressionen von PSK-Präproproteingenen und PSKR1 wurden in Wurzeln, Hypokotylen und reproduktiven Organen und nach Verwundung nachgewiesen. In diesen Geweben kann PSK-a wahrscheinlich synthetisiert und perzipiert werden. PSK- a förderte konzentrationsabhängig die Streckung der Zellen von Wurzeln und Hypokotylen von Arabidopsis-Keimlingen. Die Regulation des Wurzelwachstums durch PSK-a erfolgte über beide PSK-Rezeptoren, während das Hypokotylwachstum und die Expansion von Protoplasten, die aus dem etiolierten Hypokotyl isoliert wurden, nur über PSKR1 reguliert wurden. Analysen von T-DNA-Insertionslinien für PSKR1 zeigten, dass PSK-a und PSKR1 während der Reproduktion die Pollenschlauchorientierung und das synchrone Wachstum von Staubblättern und Fruchtknoten regulieren. PSK-a ist außerdem in die Antwort auf Verwundung und Befall durch Pathogene involviert. Über bioinformatische Analysen wurden Gene identifiziert, die mit PSKR1 und PSKR2 koexprimiert sind. Koexprimierte Kandidatengene wurden an Hand von Knockout Linien auf eine mögliche Funktion bei der Regulation von Hypokotyl- und Wurzelwachstum durch PSK-a untersucht. PSI1 ist ein Protein mit unbekannter Funktion, das möglicherweise eine Komponente des PSK-Signalweges ist. psi1-1 Keimlinge hatten kürzere Wurzeln und Hypokotyle und pskr1-3/pskr2-1/psi1-1 Dreifachmutanten zeigten einen nicht-additiven Wachstumsphänotyp

Phytosulfokine-α Controls Hypocotyl Length and Cell Expansion in Arabidopsis thaliana through Phytosulfokine Receptor 1

The disulfated peptide growth factor phytosulfokine-α (PSK-α) is perceived by LRR receptor kinases. In this study, a role for PSK signaling through PSK receptor PSKR1 in Arabidopsis thaliana hypocotyl cell elongation is established. Hypocotyls of etiolated pskr1-2 and pskr1-3 seedlings, but not of pskr2-1 seedlings were shorter than wt due to reduced cell elongation. Treatment with PSK-α did not promote hypocotyl growth indicating that PSK levels were saturating. Tyrosylprotein sulfotransferase (TPST) is responsible for sulfation and hence activation of the PSK precursor. The tpst-1 mutant displayed shorter hypocotyls with shorter cells than wt. Treatment of tpst-1 seedlings with PSK-α partially restored elongation growth in a dose-dependent manner. Hypocotyl elongation was significantly enhanced in tpst-1 seedlings at nanomolar PSK-α concentrations. Cell expansion was studied in hypocotyl protoplasts. WT and pskr2-1 protoplasts expanded in the presence of PSK-α in a dose-dependent manner. By contrast, pskr1-2 and pskr1-3 protoplasts were unresponsive to PSK-α. Protoplast swelling in response to PSK-α was unaffected by ortho-vanadate, which inhibits the plasma membrane H+-ATPase. In maize (Zea mays L.), coleoptile protoplast expansion was similarly induced by PSK-α in a dose-dependent manner and was dependent on the presence of K+ in the media. In conclusion, PSK-α signaling of hypocotyl elongation and protoplast expansion occurs through PSKR1 and likely involves K+ uptake, but does not require extracellular acidification by the plasma membrane H+-ATPase

The Research Process of PSK Biosynthesis, Signaling Transduction, and Potential Applications in Brassica napus

Phytosulfokine (PSK) is a disulfated pentapeptide that acts as a growth regulator to control plant growth and development as well as adaptability to biotic and abiotic stress. In the last three decades, PSK has drawn increasing attention due to its various functions. Preproproteins that have been tyrosine sulfonylated and then cleaved by specific enzymes contribute to mature PSK. To transfer a signal from the apoplast to the inner cells, the PSK peptide must bind to the PSK receptors (PSKR1 and PSKR2) at the cell surface. The precise mechanism of PSK signal transduction is still unknown, given that PSKR combines receptor and kinase activity with a capacity to bind calmodulin (CaM). The binding of PSK and PSKR stimulates an abundance of cGMP downstream from PSKR, further activating a cation-translocating unit composed of cyclic nucleotide-gated channel 17 (CNGC17), H+-ATPases AHA1 and AHA2, and BRI-associated receptor kinase 1 (BAK1). Recently, it has been revealed that posttranslational ubiquitination is closely related to the control of PSK and PSKR binding. To date, the majority of studies related to PSK have used Arabidopsis. Given that rapeseed and Arabidopsis share a close genetic relationship, the relevant knowledge obtained from Arabidopsis can be further applied to rapeseed

Tyrosylprotein sulfotransferase-dependent and -independent regulation of root development and signaling by PSK LRR receptor kinases in Arabidopsis

Abstract Tyrosine-sulfated peptides are key regulators of plant growth and development. The disulfated pentapeptide phytosulfokine (PSK) mediates growth via leucine-rich repeat receptor-like kinases, PSKR1 and PSKR2. PSK receptors (PSKRs) are part of a response module at the plasma membrane that mediates short-term growth responses, but downstream signaling of transcriptional regulation remains unexplored. In Arabidopsis, tyrosine sulfation is catalyzed by a single-copy gene (TPST; encoding tyrosylprotein sulfotransferase). We performed a microarray-based transcriptome analysis in the tpst-1 mutant background that lacks sulfated peptides to identify PSK-regulated genes and genes that are regulated by other sulfated peptides. Of the 169 PSK-regulated genes, several had functions in root growth and development, in agreement with shorter roots and a higher lateral root density in tpst-1. Further, tpst-1 roots developed higher numbers of root hairs, and PSK induced expression of WEREWOLF (WER), its paralog MYB DOMAIN PROTEIN 23 (MYB23), and At1g66800 that maintain non-hair cell fate. The tpst-1 pskr1-3 pskr2-1 mutant showed even shorter roots, and higher lateral root and root hair density than tpst-1, revealing unexpected synergistic effects of ligand and PSKR deficiencies. While residual activities may exist, overexpression of PSKR1 in the tpst-1 background induced root growth, suggesting that PSKR1 may be active in the absence of sulfated ligands.</jats:p

TPST-dependent and -independent regulation of root development and signaling by PSK LRR receptor kinases in Arabidopsis

AbstractTyrosine-sulfated peptides are key regulators of plant growth and development. The disulfated pentapeptide phytosulfokine (PSK) mediates growth via leucine-rich repeat receptor-like kinases, PSKR1 and PSKR2. PSKRs are part of a response module at the plasma membrane that mediates short-term growth responses, but downstream signaling of transcriptional regulation remains unexplored. In Arabidopsis, tyrosine sulfation is catalyzed by a single-copy gene (TPST). We performed a microarray-based transcriptome analysis in thetpst-1mutant background that lacks sulfated peptides to identify PSK-regulated genes and genes that are regulated by other sulfated peptides. Of the 160 PSK-regulated genes, several had functions in root growth and development in agreement with shorter roots and a higher lateral root density intpst-1. Further,tpst-1roots developed higher numbers of root hairs and PSK induced expression ofWEREWOLF (WER), its paralogMYB DOMAIN PROTEIN 23 (MYB23)andAt1g66800that maintain non-hair cell fate. Thetpst-1 pskr1-3 pskr2-1mutant showed even shorter roots, and higher lateral root and root hair density thantpst-1revealing unexpected synergistic effects of ligand and PSK receptor deficiencies. While residual activities may exist, overexpression ofPSKR1in thetpst-1background induced root growth suggesting that PSKR1 may be active in the absence of sulfated ligands.HighlightPhytosulfokine (PSK) receptor signaling promotes root elongation, determines lateral root density and maintains non-hair cell fate partially independent of TPST responsible for the activating sulfation of PSK.</jats:sec

Phytosulfokine (PSK) precursor processing by subtilase SBT3.8 and PSK signaling improve drought stress tolerance in Arabidopsis

Abstract Increasing drought stress poses a severe threat to agricultural productivity. Plants, however, have evolved numerous mechanisms to cope with such environmental stress. Here we report that the stress-induced production of a peptide signal contributes to stress tolerance. The expression of phytosulfokine (PSK) peptide precursor genes, and transcripts of three subtilisin-like serine proteases, SBT1.4, SBT3.7, and SBT3.8, were found to be up-regulated in response to osmotic stress. Stress symptoms were more pronounced in sbt3.8 loss-of-function mutants and could be alleviated by PSK treatment. Osmotic stress tolerance was improved in plants overexpressing the PSK1 precursor (proPSK1) or SBT3.8, resulting in higher fresh weight and improved lateral root development in transgenic plants compared with wild-type plants. We further showed that SBT3.8 is involved in the biogenesis of the bioactive PSK peptide. ProPSK1 was cleaved by SBT3.8 at the C-terminus of the PSK pentapeptide. Processing by SBT3.8 depended on the aspartic acid residue directly following the cleavage site. ProPSK1 processing was impaired in the sbt3.8 mutant. The data suggest that increased expression of proPSK1 in response to osmotic stress followed by the post-translational processing of proPSK1 by SBT3.8 leads to the production of PSK as a peptide signal for stress mitigation.</jats:p

Precursor processing by SBT3.8 and phytosulfokine signaling contribute to drought stress tolerance in Arabidopsis

AbstractIncreasing drought stress poses a severe threat to agricultural productivity. Plants, however, evolved numerous mechanisms to cope with such environmental stress. Here we report that the stress-induced production of a peptide signal contributes to stress tolerance. The expression of phytosulfokine (PSK) peptide precursor genes, and transcripts of three subtilisin-like serine proteases, SBT1.4, SBT3.7 and SBT3.8 were found to be up-regulated in response to osmotic stress. Stress symptoms were enhanced in sbt3.8 loss-of-function mutants and could be alleviated by PSK treatment. Osmotic stress tolerance was improved in plants overexpression the precursor of PSK1 (proPSK1) or SBT3.8 resulting in higher fresh weight and improved lateral root development in the transgenic compared to wild-type plants. We further showed that SBT3.8 is involved in the biogenesis of the bioactive PSK peptide. ProPSK1 was cleaved by SBT3.8 at the C-terminus of the PSK pentapeptide. Processing by SBT3.8 depended on the aspartic acid residue adjacent to the cleavage site. ProPSK1 processing was impaired in the sbt3.8 mutant. The data suggest that increased expression in response to osmotic stress followed by the post-translational processing of proPSK1 by SBT3.8 leads to the production of PSK as a peptide signal for stress mitigation.HighlightThe expression of phytosulfokine precursor genes and processing by the subtilase SBT3.8 are upregulated in response to osmotic stress for improved drought tolerance in Arabidopsis.</jats:sec