Somatic embryo formation in Arabidopsis and eggplant is associated with expression of a glycine-rich protein gene (Atgrp-5)

The isolation of embryogenesis-associated genes and the characterization of their roles during embryo development are important steps towards the eluc idation of the molecular mechanisms controlling embryo morphogenesis. Somat ic embryogenesis continues to be an effective model for studying gene expre ssion in embryo development. We report the analysis of the transcriptional expression of a glycine-rich gene (Atgrp-5) during somatic embryo morphogen esis. Arabidopsis thaliana transgenic lines carrying chimeric constructs co ntaining the beta -glucuronidase (GUS) reporter gene under the control of t he Atgrp-5 promoter were used to analyze its expression pattern during soma tic embryogenesis. To evaluate whether Atgrp-5 expression observed in Arabi dopsis reflects a general pattern during somatic embryogenesis, transgenic eggplant (Solanum melongena L.) was used as non-homologous embryogenic syst em. High promoter activity was detected in all cells of pro-embryogenic cel l clusters and somatic embryos from globular to torpedo stages. During the transition from torpedo to cotyledonar stage the Atgrp-5 gene was gradually turned off and, in mature embryos, its promoter activity was restricted to the protoderm. mRNA in situ hybridization on Arabidopsis somatic embryo cu ltures have confirmed the expression pattern observed by GUS histochemical assays. These results indicate that Atgrp-5 is expressed in cells that unde rgo the first anatomical modifications leading to somatic embryo developmen t. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.