Abstract
Galactinol synthase (GolS; EC 2.4.1.123) is a member of the glycosyltransferase eight family that catalyzes the first step in the biosynthesis pathway of the raffinose family of oligosaccharides (RFOs). The accumulation of RFOs in response to abiotic stress indicates a role for RFOs in stress adaptation. To obtain information on the roles of RFOs in abiotic stress adaptation in trees, we investigated the expression patterns of nine Populus trichocarpa GolS (PtrGolS) genes with special reference to stress responses. PtrGolS genes were differentially expressed in different organs, and the expressions of PtrGolS4 and PtrGolS6 were relatively high in all tested organs. The expression levels of all PtrGolS genes, except PtrGolS9, changed in response to abiotic stress in gene- and stress-type-specific manners. Moreover, short- and long-term stress treatments revealed that induction of PtrGolS by salt stress is obvious only in the early period of treatment (within 24 h), whereas water-deficit stress treatments continued to upregulate PtrGolS gene expression after two days of treatment, in addition to induction within 24 h of treatment. Consistent with these expression patterns, the galactinol content in leaves increased after four days of drought stress, but not under salt stress. Our findings suggest divergent roles for PtrGolS genes in abiotic stress responses in poplars.Electronic supplementary materialThe online version of this article (doi:10.1007/s10265-013-0597-8) contains supplementary material, which is available to authorized users.
Highlights
Abiotic stresses trigger a series of responses in plants starting with stress perception, leading to activation of signaling pathways and alteration of gene expression levels, resulting in altered plant physiology, growth and development (Loescher 2010)
Populus trichocarpa GolS (PtrGolS) genes were differentially expressed in different organs, and the expressions of PtrGolS4 and PtrGolS6 were relatively high in all tested organs
The phylogenetic analysis showed that PtrGolS proteins are distributed in four clades, suggesting that PtrGolS genes evolved from four ancestors (Fig. 2; Philippe et al 2010)
Summary
Abiotic stresses trigger a series of responses in plants starting with stress perception, leading to activation of signaling pathways and alteration of gene expression levels, resulting in altered plant physiology, growth and development (Loescher 2010). One of the adaptation mechanisms of plant cells is the production of regulatory compounds to protect cells against the effects of osmotic, cold and abiotic stresses. These compounds are known as compatible solutes; mannitol, proline and a large number of soluble oligosaccharides, such as trehalose, raffinose and stachyose (Cuin and Shabala 2008), are examples of compatible solutes responding to abiotic stresses. RFOs are composed of alpha-galactosyl derivatives of sucrose. Raffinose is the most common RFO, composed of galactose, fructose and glucose and is synthesized by the donation of galactose from galactinol, a conjugate of myo-inositol and galactose, to sucrose by raffinose synthase (RAFS; EC 2.4.1.82). The amount of galactinol was reported to exhibit seasonal changes and to increase under cold conditions (Bachmann et al 1994, Miao et al 2007)
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