Overexpression of phytosulfokine-α induces male sterility and cell growth by regulating cell wall development in Arabidopsis

Over-production of functional PSK-alpha in Arabidopsis caused increases in both plant cell growth and biomass and induced male sterility by regulating cell wall development. Phytosulfokine-alpha (PSK-alpha) is a novel disulfated pentapeptide hormone that is involved in promoting plant cell growth. Although a role for PSK-alpha in stimulating protoplast expansion has been suggested, how PSK-alpha regulates cell growth in planta remains poorly understood. In this study, we found that overexpression of the normal PSK-alpha precursor gene AtPSK4, which resulted in high levels of PSK-alpha, caused longer roots and larger leaves with enlarged cells. As expected, these changes were not observed in transgenic plants overexpressing mutated AtPSK4, which generated unsulfated PSK-alpha. These findings confirmed the role of PSK-alpha in promoting plant cell growth. Furthermore, we found that overexpressing AtPSK4, but not mutated AtPSK4, induced a phenotype of male sterility that resulted from the failure of fibrous cell wall development in the endothecium. In addition, overexpressing AtPSK4 enhanced expression of a number of genes encoding expansins, which are involved in cell wall loosening. Accordingly, in addition to its role in cell growth, we propose a novel function for PSK-alpha signaling in the modulation of plant male sterility via regulation of cell wall development.