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

Abstract

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.

Soluble carbohydrates in developing and mature diaspores of polar Caryophyllaceae and Poaceae

“…Higher levels of GolS expression and GolS activity are characteristic of the middle phase of reserve accumulation, but they were found to decrease in soybeans (Saravitz et al 1987), peas ) and vetch (Lahuta 2006), and increase in corn (Zhao et al 2004a) in successive stages of seed maturation. Accelerated desiccation of mature corn seeds increases ZmGOLS expression and GolS activity (Zhao et al 2004b). The expression of ZmGOLS2, which encodes tissue responses to dehydration stress, is positively correlated with myo-inositol concentrations (Zhao et al 2004b).…”

“…Accelerated desiccation of mature corn seeds increases ZmGOLS expression and GolS activity (Zhao et al 2004b). The expression of ZmGOLS2, which encodes tissue responses to dehydration stress, is positively correlated with myo-inositol concentrations (Zhao et al 2004b). Numerous copies of GolS genes, which were detected in vegetative tissues of Arabidopsis thaliana (Nishizawa et al 2008), Salvia miltiorrhiza (Wang et al 2012) and Coffea arabica (Dos Santos et al 2011), are specifically expressed in response to abiotic stressors such as salinification, cold, dehydration and soil drought.…”

Phloem loading in Verbascum phoeniceum L. depends on the synthesis of raffinose-family oligosaccharides

“…Highest amino acid homology (87%) is with the gene from A. reptans, which is most closely related to V. phoeniceum. Translated sequences for both cDNAs contained the putative serine phosphorylation site (residues 254 and 261 in VpGAS1 and VpGAS2, respectively) found in many GAS sequences (15), as well as a hydrophobic motif, APSAA, at the carboxyl terminal, which has been found in all reported GAS sequences (15)(16)(17)(20)(21)(22)(23).…”

Enzymatic breakdown of raffinose oligosaccharides in pea seeds

“…During slow drying of imbibed seeds, RFOs can be re-synthesized by the machinery for RFO synthesis, which is still active during early germination, as demonstrated by labelling studies (Dey 1985 and references therein). Of the involved enzymes, galactinol synthase (in maize; Zhao et al 2004) and stachyose Peterbauer et al 1999) were both active during the entire period of RFO breakdown, although transcripts declined rapidly after imbibition. After radicle emergence, however, drying damages the seedling irreversibly (Nonogaki 2006).…”