title: Activation of gibberellin biosynthesis and response pathways by low temperature during imbibition of Arabidopsis thaliana seeds.
abstract: Exposure of imbibed seeds to low temperature (typically 4 degrees C) is widely used to break seed dormancy and to improve the frequency of germination. However, the mechanism by which temperature accelerates germination is largely unknown. Using DNA microarray and gas chromatography-mass spectrometry analyses, we found that a subset of gibberellin (GA) biosynthesis genes were upregulated in response to low temperature, resulting in an increase in the level of bioactive GAs and transcript abundance of GA-inducible genes in imbibed Arabidopsis thaliana seeds. Using a loss-of-function mutant, the cold-inducible GA biosynthesis gene, AtGA3ox1, was shown to play an essential role in mediating the effect of low temperature. Besides temperature, AtGA3ox1 also is positively regulated by active phytochrome and negatively regulated by GA activity. We show that both red light and GA deficiency act in addition to low temperature to elevate the level of AtGA3ox1 transcript, indicating that multiple signals are integrated by the AtGA3ox1 gene to control seed germination. When induced by low temperature, AtGA3ox1 mRNA was detectable by in situ RNA hybridization in an additional set of cell types relative to that in red light-induced seeds. Our results illustrate that the GA biosynthesis and response pathways are activated during seed imbibition at low temperature and suggest that the cellular distribution of bioactive GAs may be altered under different light and temperature conditions.
authors.affiliation: Plant Science Center, RIKEN, Institute of Physical and Chemical Research, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan.
authors.forename: Yukika
authors.initials: Y
authors.lastname: Yamauchi
authors.forename: Mikihiro
authors.initials: M
authors.lastname: Ogawa
authors.forename: Ayuko
authors.initials: A
authors.lastname: Kuwahara
authors.forename: Atsushi
authors.initials: A
authors.lastname: Hanada
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kamiya
authors.forename: Shinjiro
authors.initials: S
authors.lastname: Yamaguchi
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D003080:Cold Temperature; D015971:Gene Expression Regulation, Enzymologic / Q000528:radiation effects; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D018525:Germination / Q000502:physiology*; D005875:Gibberellins / Q000096:biosynthesis*; D017403:In Situ Hybridization; D008027:Light; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010834:Phytochrome / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012639:Seeds / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology
chemical_list: D005875:Gibberellins; D012333:RNA, Messenger; D010834:Phytochrome; D006899:Mixed Function Oxygenases; C108186:gibberellin 3beta-hydroxylase