A PLANT GENE WITH HOMOLOGY TO D-MYO-INOSITOL-3-PHOSPHATE SYNTHASE IS RAPIDLY AND SPATIALLY UP-REGULATED DURING AN ABSCISIC-ACID-INDUCED MORPHOGENIC RESPONSE IN SPIRODELA-POLYRRHIZA

The induction of turions (dormant vegetative buds) by the plant growth regulator abscisic acid (ABA) in the aquatic angiosperm Spirodela polyrrhiza is one of the few examples of a plant hormone triggering a morphogenic response. In order to aid our understanding of the molecular basis of this phenomenon a cDNA library has been prepared from ABA-induced S. polyrrhiza and by differential screening a number of early ABA-up-regulated genes have been isolated. This paper reports the characterization of one such cDNA (tur1) from S. polyrrhiza which codes for a protein highly homologous to yeast D-Myo-inositol-3-phosphate synthase (EC.5.5.1.4), the catalyst for the first committed step in inositol biosynthesis. This is the first reported cloning of a plant gene involved in inositol production. It is shown by Northern analysis and in situ hybridization that ABA induces a rapid preferential up-regulation of this gene and that this is localized to the stolon tissue. The stolon connects the developing turion to the node of the mother frond (the meristematic region involved in the production of turions which arise as a morphogenic response to this hormone). This increase in tur1 transcript level is accompanied by a rise in the activity of D-myo-inositol-3-phosphate synthase. The possible role of inositol in ABA-induced events during turion formation is discussed.