Expression of the maize GALACTINOL SYNTHASE gene family: (I) Expression of two different genes during seed development and germination

GALACTINOL SYNTHASE (GOLS) acts on UDP-galactose and myo-inositol to form galactinol. The production of galactinol is thought to be the committed step in the biosynthesis of the raffinose family oligosaccharides (RFOs), a group of carbohydrates hypothesized to play a number of roles in plant development. Three cDNAs for maize (Zea mays L. inbred line B73) GOLS (ZmGOLS) were identified from the Pioneer Hi-Bred expressed sequence database. The recombinant proteins from these cDNAs synthesize galactinol. Transcript amounts in developing and germinating seeds were determined using northern blot, ribonuclease protection assays, and multiplex RT-PCR. ZmGOLS1 mRNA was not detected in any of the tissues examined. ZmGOLS3 transcripts accumulated late during seed development and were present in mature seeds but declined quickly to undetectable amounts following imbibition. Experiments in which germination was interrupted by desiccation, but not by cold, heat, or salt stress, detected ZmGOLS2 transcripts. Soluble sugar amounts and GALACTINOL SYNTHASE activity were determined for developing maize seeds as well as for mature seeds during germination and upon stress during germination. Neither enzyme activity nor galactinol or raffinose quantities could be related to ZmGOLS transcript abundance. Galactinol amounts were most closely related to myo-inositol quantities during development and early germination. Maturation desiccation appears to be a switch delineating a realm of expression for ZmGOLS3, predominant during seed development, from that of ZmGOLS2, principally associated with post-imbibition dehydration stress.