Isolation and characterization of an embryo-specific Em-like gene of pedunculate oak (Quercus robur L.) and its temporal and spatial expression patterns during somatic and zygotic embryo development

The oak Em gene, QrEm, was isolated from Quercus robur L. zygotic embryos in RT-PCR using degenerate primers. The full-length cDNA was obtained by RACE. Sequence analyses revealed a high degree of similarity to previously identified Em-like genes from both monocots and dicots. Northern blot analyses showed that QrEm gene is expressed in zygotic embryos during the mid-maturation phase, with a decline following towards the end of seed development. In somatic embryos, abundant transcript accumulation was observed after treatment with 6% sorbitol or after partial desiccation. In situ hybridization experiments displayed similar tissue-specific expression patterns in both zygotic and somatic embryos, predominantly in the meristematic regions of root and shoot apices as well as provascular tissues, whereas almost no hybridization signal was found in the cotyledons. Wounding, drought and cold all failed to induce expression of the QrEm gene in vegetative tissue, suggesting that the QrEm gene is embryo-specific and its expression is developmentally regulated.