The peptide growth factor Phytosulphokine-alpha controls root growth and reproductive processes in Arabidopsis thaliana

Phytosulfokin-alpha (PSK-alpha) ist ein bisulfatiertes Pentapetid, welches als Wachstumsfaktor die Proliferation von Zellen in Zellkultur niedriger Dichte stimuliert. In der vorliegenden Arbeit wurden physiologische und genetische Ansätze verfolgt, um Funktionen von PSK-alpha in Arabidopsis thaliana aufzuklären. Promotor-GUS Expressionsanalysen der PSK-Präproproteingene und des PSK-Rezeptorgens AtPSKR1 in Wurzeln und Blüten deuteten auf mögliche Funktionen von PSK-alpha in diesen Geweben hin. Exogen appliziertes PSK-alpha förderte das Wurzelwachstum von Arabidopsiskeimlingen. Das Wurzelwachstum der PSK-Rezeptor T-DNA Insertionsmutante Atpskr1-T war inhibiert. Diese Ergebnisse zeigten, dass PSK-alpha in die Regulation von Wurzelwachstum involviert ist. Charakteristisch für die Atpskr1-T Mutante war eine verringerte Samenbildung im Vergleich zu Wildtyppflanzen. Genetische Analysen zeigten, dass sowohl ein paternaler als auch maternale Effekte und asynchrones Wachstum der inneren Blütenorgane zur Ausbildung des Mutantenphänotyps führen.Phytosulfokine-alpha (PSK-alpha) is a disulfated pentapeptide that was shown previously to act as growth factor in in vitro cultured plant cells kept at low density. The aim of this work was to analyse functions of PSK-alpha in planta. Arabidopsis was chosen as a model plant to perform functional analysis using both, physiological and genetic approaches. Promoter:GUS analysis revealed expression of PSK precursor genes and of the PSK receptor gene AtPSKR1 in roots and flowers. Application of PSK-alpha to growing seedlings resulted in increased root mass. On the other hand, the PSK receptor knock out mutant Atpskr1-T showed reduced growth rates confirming a role of PSK-alpha signaling in root growth regulation. The receptor knock out mutant was not only impaired in root growth but also in reproductive success. Genetic analysis indicated that paternal as well as maternal effects and asynchronous growth of the inner flower organs strongly effects seed formation in Atpskr1-T plants

PSK-alpha promotes root growth in Arabidopsis

Phytosulfokine-alpha (PSK-alpha) is a disulfated pentapeptide described to act as a growth factor in suspension cells. In this study, the involvement of PSK signaling through the PSK receptor gene AtPSKR1 in Arabidopsis root growth was assessed. Expression studies of PSK precursor genes and of AtPSKR1 were performed in roots with RT-PCR and P:GUS analyses. Root elongation, lateral root formation, cell production and root cell elongation were analyzed in wild-type (wt) and in the receptor knockout mutant Atpskr1-T treated with or without synthetic PSK-alpha. Phytosulfokine and AtPSKR1 genes are differentially expressed in roots. PSK-alpha induced root growth in a dose-dependent manner without affecting lateral root density. Kinematic analysis established that enhancement of root growth by PSK-alpha was mainly caused by an increase in cell size. In Atpskr1-T, the primary roots were shorter as a result of reduced mature cell size and a smaller root apical meristem composed of fewer cells than in wt. The results indicate that PSK-alpha signaling through AtPSKR1 affects root elongation primarily via control of mature cell size. Root organogenesis, on the other hand, is not controlled by PSK-alpha