Isolation of a gene preferentially expressed in heart-shaped embryos of tobacco (Nicotiana tabacum)

We constructed two tobacco cDNA libraries from 200 microdissected undiffere ntiated globular proembryos and 150 just-differentiating heart-shaped embry os using the RT PCR technique. Through differential screening of the two cD NA libraries, a cDNA clone, designated THE3 (tobacco heart-shaped embryo 3) , was sequenced and analyzed. The deduced amino acid sequence encodes a bas ic protein (pI 10.88) of 40.6 kDa and contains a putative nuclear targeting signal sequence. Through the whole-mount in situ hybridization, the transc ript corresponding to THE3 gene shows preferential expression in heart-shap ed embryos but is weakly expressed in globular proembryos. The spatial and temporal expression of the THE3 gene suggests that it may play a role durin g proembryo differentiation.