Abstract
Seed dormancy and germination are controlled by multiple environmental and endogenous factors. In Arabidopsis, both gibberellin (GA) and cold treatment (imbibition at 4℃ in the dark) promote seed germination. We have previously shown that the GA biosynthesis gene, AtGA3ox1,encoding a GA3-oxidase, is upregulated in response to cold treatment. Consistent with the increase in AtGA3ox1 expression, endogenous GA_4 content and the level of GA-responsive transcripts were elevated following cold treatment. To predict how cold treatment stimulates germination through GA action, GA-dependent gene expression during cold treatment was monitored using DNA microarray analysis. We have previously analyzed gene expression profiles during (A) wild-type seed germination at 22℃ in the light, and (B) germination of GA-deficient ga1-3 mutant seeds upon exogenous GA treatment (22℃, light). These microarray data indicated that the majority of GA-responsive genes during cold treatment were categorized into a gene group of which expression is up-or down-regulated at early time points after imbibition of wild-type seeds (A). We also found that 25% of GA-regulated genes during cold treatment have previously been classified as GA-responsive genes in ga1-3 seeds (B). The rest of GA-regulated genes during cold treatment appear to be unique to the low temperature environment. In addition, we noted that only a few genes responded to 4℃ commonly at seed germination and seedling stages, based on microarray data reported by other groups. These results suggest that both GA biosynthesis and response are modulated under different environmental conditions to control seed germination, and that the response to low temperature is altered at different developmental stages.
