Submitted to: Plant Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/5/2005
Publication Date: 7/27/2005
Citation: Maul, D.P., Bausher, M.G., Mccollum, T.G., Mozoruk, J.J., Niedz, R.P. 2005. Identification of a gene induced during early somatic embryogenesis in valencia sweet orange (citrus sinensis l. osbeck) that encodes a putative histidine-containing phosphotransmitter protein. Plant Science. Interpretive Summary: Somatic embryogenesis in plants is the process of producing embryos from non-sexual cells, or from sexual cells that have not undergone fertilization. Because it closely resembles the process of embryogenesis as it occurs normally in the plant, somatic embryogenesis is an attractive system to study changes of gene expression that take place during the early stages of development. In sweet orange, somatic embryos can be induced by supplementing the nutrient media with glycerol. In order to identify embryogenesis-associated genes, and using the technique known as differential display, we compared gene expression patterns in a sweet orange somatic embryogenesis system before and after embryo formation. We have isolated and characterized a gene, named CsEP (for Citrus sinensis Embryogenic Protein), that is homologous to a histidine-containing phosphotransmitter family of proteins in Arabidopsis thaliana. Identifying changes in gene expression during somatic embryogenesis will allow us to understand molecular mechanisms that control embryogenesis and will eventually lead us to direct desirable changes in Citrus embryos.
Technical Abstract: A cDNA named CsEP (for Citrus sinensis Embryogenic Protein) containing a conserved domain characteristic of a two-component phosphorelay intermediate associated with signal transduction mechanisms was isolated from globular embryos of Valencia sweet orange by differential display RT-PCR. The corresponding full-length cDNA, subsequently obtained by RACE-PCR, is 772 bp long and contains a 450 bp open reading frame encoding a 150 amino acid protein. The deduced amino acid sequence of CsEP is approximately 60 % homologous to five AHP histidine-containing phosphotransmitter proteins (AHP1 through AHP5) in Arabidopsis thaliana. RT-PCR analyses showed higher CsEP transcript abundance in embryogenic calli when compared to non-embryogenic calli. CsEP transcription was also higher in embryogenic calli than in leaves, phloem, roots, and flavedo (rind). Immature fruits and mature flowers, both of which contain tissues with embryogenic potential, showed increased CsEP expression. Southern blot analysis revealed that the CsEP gene seems to be present as a single copy in the C. sinensis genome. Results of this study provide insight on signal transduction mechanisms that may be active during plant embryogenesis.