Isolation and molecular characterization of genes expressed during somatic embryo development in Pinus radiata

Pinus radiata somatic embryogenic tissue offers many advantages over seed material for plantation forestry. Although much progress has been made in embryogenesis during the past few years, more research is needed to understand mechanisms underlying the difference in response by genotypes and the conversion of immature to mature embryos. As an initial genetic characterization of early embryo development in P. radiata, a cDNA library was constructed using mRNA from cultured tissue that was forming stage 1 embryos. This library was differentially screened against non-embryogenic tissues ( roots, shoots and needles) and six gene families preferentially expressed during conifer embryogenesis were identified. These genes showed high mRNA transcript levels in embryogenic tissue and little or no expression in non-embryogenic ( roots, shoots and needles) or callus tissue ( needle and fibre culture callus). These gene families included four putative extracellular proteins ( germin, beta-expansin, 21 kDa protein precursor and cellulase), a cytochrome P450 enzyme and a gene with unknown function (PRE87). We report data on the copy number of these genes and examine their expression in both P. radiata and Picea abies embryogenic tissues.