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 pol yrrhiza is one of the few examples of a plant hormone triggering a mor phogenic response. In order to aid our understanding of the molecular basis of this phenomenon a cDNA library has been prepared from ABA-ind uced S. polyrrhiza and by differential screening a number of early ABA -up-regulated genes have been isolated. This paper reports the charact erization of one such cDNA (tur1) from S. polyrrhiza which codes for a protein highly homologous to yeast D-Myo-inositol-3-phosphate synthas e (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 invol ved in inositol production. It is shown by Northern analysis and in si tu hybridization that ABA induces a rapid preferential up-regulation o f this gene and that this is localized to the stolon tissue. The stolo n 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 tran script level is accompanied by a rise in the activity of D-myo-inosito l-3-phosphate synthase. The possible role of inositol in ABA-induced e vents during turion formation is discussed.