低温ストレスはイネのガラクチノール合成酵素遺伝子の発現を誘導する

抄録

The raffinose family oligosaccharides (RFOs) are supposed to play a number of roles in plant development and stress tolerance. Galactinol synthase (GolS) catalyzing UDP-galactose and myo-inositol to form galactinol is a key enzyme in the raffinose synthesis pathway. Recently, it has been reported that the expression of enzymes related to the biosynthesis of galactinol and RFOs and their intracellular accumulation in plant cells are involved in acquired tolerance to various stresses. A rice GolS-homolog was found to be expressed in rice under drought stress, but it is unclear whether or not temperature stress changes the expression levels of rice GolS. By semi-quantitative RT-PCR, we analyzed the expression profiles of two GolS homologs in rice seedlings under chilling and salt stress. The predicted protein of OsGolS1 revealed a high similarity to those of OsGolS2 (78% in amino acid identity), AtGolS1 and AtGolS3 (72% and 67%, respectively). Chilling and salt stress induced mRNAs of OsGolS1 but not OsGolS2. It has been reported that an oxidative stress specific heat shock factor (HSFA2)is involved in the induction of AtGolS1 mRNA under heat stress via generation of reactive oxygen species (ROS). In this study, we examined whether HSFA2 functions in the induction of OsGolS1 in response to chilling stress. The expression level of rice HSFA2 homolog did not change under chilling stress. These results suggest that induction of OsGolS1 is involved in chilling stress response of rice and that expression of OsGolS1 at low temperature is regulated at downstream of OsMyb4 rather than DREB/CBF or HSFA2.