High accumulation of legumin and Lea-like mRNAs during maturation is associated with increased conversion frequency of somatic embryos from pedunculate oak (Quercus robur L.).

The expression patterns of the storage protein legumin gene and Em- and dehydrin-like homologues were investigated in somatic embryos from Quercus robur L. The effect of different maturation treatments (1% agar, 6% sorbitol, or 5% polyethylene glycol) and partial desiccation on transcript accumulations as well as conversion capacity of somatic embryos was also investigated. Differential expression of putative Em- and two dehydrin-like homologues (designated as Dhn1a and Dhn1b) was detected in somatic oak embryos with heterologous probes. Low expression levels of legumin, Em- and dehydrin-like mRNAs were detected in somatic embryos prior to maturation treatment. A high accumulation of these transcripts was found in embryos that had been cultured on media supplemented with 6% sorbitol or 1% agar. These embryos also showed a high conversion frequency into plantlets. In contrast, no improvement in plant conversion as well as a low accumulation of legumin, Em-like and Dhn1b-like transcripts was observed in embryos that were matured on polyethylene glycol medium. Partial-desiccation treatment significantly enhanced the plant conversion. Nevertheless, a decline in expression of legumin, Em-like and Dhn1a-like homologues was detected upon dehydration. In contrast, Dhn1b and oak homologues to peach dehydrin were also strongly expressed in desiccated embryos. In addition, the treatment of embryos with abscisic acid promoted the accumulation of all investigated transcripts. These results suggest that the regulation of the legumin storage protein gene and Lea-like homologues in somatic oak embryos is under developmental control and that their regulation can be influenced by manipulating the culture conditions.