Gibberellin Biosynthesis and Response during Arabidopsis Seed Germination[W]

Abstract

The hormone-mediated control of plant growth and development involves both synthesis and response. Previous studies have shown that gibberellin (GA) plays an essential role in Arabidopsis seed germination. To learn how GA stimulates seed germination, we performed comprehensive analyses of GA biosynthesis and response using gas chromatography-mass spectrometry and oligonucleotide-based DNA microarray analysis. In addition, spatial correlations between GA biosynthesis and response were assessed by in situ hybridization. We identified a number of transcripts, the abundance of which is modulated upon exposure to exogenous GA. A subset of these GA-regulated genes was expressed in accordance with an increase in endogenous active GA levels, which occurs just before radicle emergence. The GA-responsive genes identified include those responsible for synthesis, transport, and signaling of other hormones, suggesting the presence of uncharacterized crosstalk between GA and other hormones. In situ hybridization analysis demonstrated that the expression of GAresponsive genes is not restricted to the predicted site of GA biosynthesis, suggesting that GA itself, or GA signals, is transmitted across different cell types during Arabidopsis seed germination.

Seed dormancy and germination

“…Experiments using GA-deficient seeds (Ogawa et al, 2003) have described temporal transcript abundance changes in GA-deficient mutants seeds stimulated to germinate by GA treatment or in nongerminating waterimbibed controls. Dormancy cycling was studied in the Arabidopsis accession Cvi in a range of dormant and after-ripening states.…”

“…However, its role in the regulation of germination and seedling establishment remained obscure (Kucera et al, 2006). Auxin alone was not generally considered to be important in the control of seed germination but cross-talk between auxin, ABA, GA and ethylene was suggested to both affect germination and seedling establishment (Fu and Harberd, 2003;Ogawa et al, 2003; Chiwocha et al, 2005, Carrera et al, 2008Liu, PP et al, 2007 reviewed by Holdsworth et al, 2008a. Analysis of the expression of the DR5:GUS auxin reporter indicated that auxin accumulates during embryogenesis and is present in the seed following imbibition.…”

“…Expression was observed at the radicle tip prior to germination in one study (Liu, PP et al, 2007) and throughout the embryo at the end of embryogenesis in another study (Ni et al, 2001). Analysis of transcriptome expression showed that RNA encoding auxin transporters AUX1, PIN2, and PIN7 were highly up-regulated in response to treatment of ga1 mutant seeds with GA (Ogawa et al, 2003), and that both efflux and influx transporters are up-regulated in after-ripened compared to dormant seeds (Carrera et al, 2008). This may indicate a role for these transporters in germination per-se, or with the establishment of the root apex and gravitropism following radicle emergence.…”

Functional analysis of a cotton glucuronosyltransferase promoter in transgenic tobaccos

“…GUS activity was hardly detected in the corresponding tissues of the negative control plants (data not shown). Consistent with the GUS activity levels, the promoter region contains several important elements, such as an amylase-box, CARE, GARE, GCN4-motif, ACGT motif and AACA motif, which are involved in seed-specific and normal embryo-specific expression [24,[28][29][30][31]39]. Quantitative GUS assays showed that the highest expression was in Functional analysis of a GhGlcAT1 promoter 180 npg the anthers, with relatively high expression in the stigmas and styles.…”

“…The amylase-box was required for high expression of the gene in the seeds [24], while the E-box was shown to be bound by bHLH (basic helix-loop-helix) transcription factors and to regulate the seed-specific expression of seed storage protein genes and the expression of genes involved in anthocyanin biosynthesis [25][26][27]. The CARE and GARE boxes were required during seed germination in Arabidopsis and rice [28,29]. In addition, a combination of GCN4, ACGT and AACA motifs was sufficient to confer a detectable level of endosperm expression in rice [30,31].…”