The results showed that ectopic expression of LEC1 and LEC2 could confer embryonic characteristics to transgenic tobacco seedling. Somatic embryogenesis and plant regeneration was occurred in a high frequency from LEC2 transgenic seedlings grown in medium without application of exogenous plant growth regulators. However, regenerated plants were not obtained from LEC1 overexpressors under the same culture condition. Ectopic expression of LEC2 activated expression of globulin, oleosin, caleosin and LEA protein genes that normally expressed predominantly in maturation seeds. Genes encoding regulators that play important roles in embryo development such as MADSbox protein 9, SERK1 and leafy cotyledon 1-like were activated in the transgenic plants. These results indicated that Arabidopsis LEC genes could activate somatic embryogenesis process in transgenic tobacco plants, albeit to different extents. To understand the mechanisms by which LEC2 gene promote somatic embryo formation, we searched for genes affected by LEC2 ectopic expression using digital gene expression profiling. As described above, 30 mM DEX could induce large amount of high quality embryonic callus. In the digital gene expression experiment, 30 mM DEX was selected for embryonic callus induction. High throughput sequencing generated about 12 million short reads, among which 5298 and 5568 unigenes were up- and downregulated in LEC2 transgenic tobacco. Genes normally expressed in embryo maturation processes are induced by ectopic LEC2 activity. For example, genes encoding seed storage proteins include 7S and 11S globulin, vicilin, oleosin, caleosin and late embryogenesis abundant protein were activated in LEC2 transgenic seedlings. Most of genes acting in fatty acid and steroid biosynthesis were up-regulated in LEC2 transgenic lines. Over expression of AtLEC1 and AtLEC2 genes was sufficient to induce somatic embryogenesis in Arabidopsis. Here we showed that expression of AtLEC1 and AtLEC2 in tobacco could activate somatic embryogenesis process, although in a different extend. Cotyledons of LEC1 transgenic tobacco were ivory and fleshy and could not expand; their hypocotyls were stubby. These results suggest that AtLEC1 can help start the transition from vegetative growth to somatic embryogenesis, but is not sufficient to complete this process in tobacco after 20 days of induction. A previous study has shown that constitutive expression of LEC1 in lec1 background by 35S promoter could induce somatic embryo formation in few transgenic lines. In our experiment, when LEC1 seedlings grown on medium containing 30 mM DEX for 40 days, most of the plants produced true leaves. The recovery of vegetative growth may be due to exhaust DEX in the medium and resulted in the cessation of LEC1 expression. Whether longer time induction on DEX medium could induce somatic embryogenesis in LEC1 transgenic tobacco is unknown.