Galactinol synthase1. A Novel Heat Shock Factor Target Gene Responsible for Heat-Induced Synthesis of Raffinose Family Oligosaccharides in Arabidopsis

Abstract

Heat shock factors (HSFs) are transcriptional regulators of the heat shock response. The major target of HSFs are the genes encoding heat shock proteins (HSPs), which are known to have a protective function that counteracts cytotoxic effects. To identify other HSF target genes, which may be important determinants for the generation of stress tolerance in Arabidopsis, we screened a library enriched for genes that are up-regulated in HSF3 (AtHsfA1b)-overexpressing transgenic plants (TPs). Galactinol synthase1 (GolS1) is one of the genes that is heat-inducible in wild type, but shows constitutive mRNA levels in HSF3 TPs. The generation and analysis of TPs containing GolS1-promoter::b-glucuronidase-reporter gene constructs showed that, upon heat stress, the expression is transcriptionally controlled and occurs in all vegetative tissues. Functional consequences of GolS1 expression were investigated by the quantification of raffinose, stachyose, and galactinol contents in wild type, HSF3 TPs, and two different GolS1 knockout mutants (gols1-1 and gols1-2). This analysis demonstrates that (1) raffinose content in leaves increases upon heat stress in wild-type but not in the GolS1 mutant plants; and (2) the level of raffinose is enhanced and stachyose is present at normal temperature in HSF3 TPs. These data provide evidence that GolS1 is a novel HSF target gene, which is responsible for heat stress-dependent synthesis of raffinose, a member of the raffinose family oligosaccharides. The biological function of this osmoprotective substance and the role of HSF-dependent genes in this biochemical pathway are discussed.

Identification and Functional Characterization of the GALACTINOL SYNTHASE (MoGolS1) Gene in Melissa officinalis Plants

“…6A and B). Our result was supported by the findings of Panikulangara et al [2004] who mentioned strong induction of GolS1 gene both in wild type (WT) and heat shock factor3 (HSF3) TPs Arabidopsis plant subjected to heat stress (37 o C) for 2h. The transcription level of MoGolS1 gene also increased at moderate level in the leaves treated with cold for 12 h or 1 day.…”

“…6A). One of the homolog of the MoGolS1, the AtGolS1 is known as a Nobel heat shock factor target gene, induced even in wild type Arabidopsis plants after heat stress [Panikulangara et al, 2004]. We therefore investigated whether our GolS1 gene (MoGolS1) was induced with heat shock treatment.…”

“…For examples, Taji et al [2002] reported that AtGolS1 and AtGolS2 was induced by drought and high salinity but AtGolS3 was induced by the cold stress, while Panikulangara et al [2004] mentioned that Arabidopsis GolS1 was heat inducible. To determine whether other types of abiotic stress also induced MoGloS1 transcription in the lemon balm plants we carried out northern hybridization purifying RNA from lemon balm leaves, stems and roots treated with 300 mM manitol or NaCl.…”

“…Although there was no report about the transcription of GolS gene by manitol, strong induction of AtGolS2 was reported by 250 mM NaCl for 2−8 h [Taji et al, 2002]. As mentioned by Taji et al [2002] and Panikulangara et al [2004] that GolS gene also induced by the heat and cold stress, we treated the lemon balm plants with heat (37 o C) or cold (4 o C) before extracting total RNA. Our northern data shows that heat stress for 3 h greatly influenced the activation of MoGolS1 transcript in the lemon balm leaves (Figs.…”

“…Over expression of Arabidopsis GolS1 and GolS2 had increased levels of galactinol and raffinose in the leaves compared with wildtype plants under control growth conditions in the transgenic plants were correlated with increased tolerance to methyl viologen (MV) treatment and salinity or chilling stress probably by scavenging hydroxyl radicals as a novel function to protect plant cells from oxidative stress [Taji et al, 2002;Nishizawa et al, 2008]. Furthermore, GolS1 in Arabidopsis is reported as a novel heat shock factor (HSF) target gene, which is responsible for heat stress-dependent synthesis of raffinose, [Panikulangara et al, 2004] and may have influence in heat shock tolerance in the plants. Although the roles of GolS genes have been elucidated in many plants, nothing is known about it in the Lemon balm (Melissa officinalis), a very important medicinal plant species.…”