Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/1/2003
Publication Date: 3/1/2003
Citation: VOLK, G.M., HARITATOS, E.E., TURGEON, R. GALACTINOL SYNTHASE GENE EXPRESSION IN MELON. AMERICAN SOCIETY FOR HORTICULTURAL SCIENCE. 2003. Vol. 128:p.8-15. Interpretive Summary: Raffinose family sugars (such as raffinose and stachyose) play a key role in melon plant development. These sugars also accumulate in response to cold, drought and salt stress in some species. Galactinol synthase is the enzyme that catalyzes the formation of galactinol, a key precursor in the formation of raffinose and stachyose. By determining when and where the galactinol synthase genes are expressed, we can better understand the roles of this enzyme in plant development. We demonstrate that the CmGAS1 gene is expressed in mature leaves and in developing seeds, while the CmGAS2 gene is expressed only in melon mature leaves. The expression of the CmGAS genes in leaves is thought to be critical for the formation of raffinose and stachyose for phloem translocation. These sugars may accumulate in seeds to protect membranes against the desiccation process that occurs during maturation.
Technical Abstract: Raffinose family oligosaccharides (RFOs) perform several physiological functions in plants. In addition to accumulating during seed formation, raffinose and stachyose are translocated in the phloem and may accumulate in response to cold, drought, or salt stress. Although the synthesis of galactinol, as mediated by galactinol synthase (GAS), is the first committed step in RFO formation its expression patterns are poorly understood in most species. We have cloned and characterized the expression of two galactinol synthase gene family members in melon, Cucumis melo L. CmGAS1 and CmGAS2 are both highly expressed in mature leaves. GAS transcription in leaves was not upregulated by either drought or cold stresses. CmGAS1 transcripts were present in developing melon seeds at a time coincident with the formation of raffinose and stachyose. Based on the GAS expression and RFO accumulation patterns, we propose that RFOs in melon function in carbon translocation and seed desiccation.