A peptide hormone gene, GhPSK promotes fibre elongation and contributes to longer and finer cotton fibre

Cotton fibres, the single-celled trichomes derived from the ovule epidermis, provide the most important natural material for the global textile industry. A number of studies have demonstrated that regulating endogenous hormone levels through transgenic approaches can improve cotton fibre qualities. Phytosulfokine-alpha (PSK-alpha) is a novel peptide hormone in plants that is involved in regulating cell proliferation and elongation. However, its potential applications in crop genetic improvement have not been evaluated. In this study, we describe how exogenous PSK-alpha application promotes cotton fibre cell elongation in vitro. Chlorate, an effective inhibitor of peptide sulfation, suppressed fibre elongation in ovule culture. Exogenously applied PSK-alpha partly restored the chlorate-induced suppression. A putative PSK gene (GhPSK) was cloned from Gossypium hirsutum. Expression pattern analysis revealed that GhPSK is preferentially expressed in rapidly elongating fibre cells (5-20 days postanthesis). Overexpression of GhPSK in cotton increased the endogenous PSK-alpha level and promoted cotton fibre cell elongation, resulting in longer and finer fibres. Further results from electrophysiological and physiological analyses suggest that GhPSK affects fibre development through regulation of K+ efflux. Digital gene expression (DGE) profile analysis of GhPSK overexpression lines indicates that PSK signalling may regulate the respiratory electron-transport chain and reactive oxygen species to affect cotton fibre development. These results imply that peptide hormones are involved in cotton fibre growth and suggest a new strategy for the biotechnological improvement of cotton fibre quality.