Overexpression of gibberellin 2-oxidase 4 from tall fescue affected plant height, tillering and drought tolerance in rice

Gibberellin (GA) is an important phytohormone that regulates plant growth and development. GA-2-oxidases (GA2oxs) have been found to affect plant height, tillering and stress tolerance by inactivating endogenous bioactive GAs. The present study aimed to isolate GA2oxs genes from tall fescue (Festuca arundinacea), analyze their expression level under abiotic stresses (10% PEG6000 induced drought stress, 150 mM NaCl induced salt stress, heat stress at 38 °C, and cold stress at 4 °C) and search for valuable genes for improving stress tolerance. Among eight FaGA2ox genes, FaGA2ox4 was found to represent a highest expression level at 24 h of PEG-induced drought stress and was chosen for further analysis. Compared with wildtype plants, transgenic rice plants overexpressing FaGA2ox4 exhibited a dwarf and high-tillering phenotype and the dwarf phenotype was partially compensated by foliar application of 10 μM GA3. In addition, transgenic plants showed improved drought stress tolerance, as manifested by higher leaf relative water content and lower electrolyte leakage than wildtype. Further qRT-PCR analysis demonstrated that the enhanced drought stress tolerance may be associated with decreased expression levels of genes involved in chlorophyll degradation (OsSGRL) and GA synthesis (OsGA3ox1) as well as increased expression of ABA-synthesizing gene (OsNCED3) in transgenic plants overexpressing FaGA2ox4.