Gibberellins: regulating genes and germination

Abstract

The range of processes regulated by gibberellins (GAs) covers all aspects of the life history of the plant from seed germination to vegetative growth and flowering. In seeds there has been an intensive search, using the techniques of both biochemistry and cell biology, for the regulatory molecules linking GA perception to gene regulation and the events of germination. Although a GA receptor has yet to be identified, the site of perception has been localized to the plasma membrane. Calmodulin, Ca2+ and cGMP have also been identified as elements of the GA signal transduction pathway. These regulators parallel many of the signalling elements identified in the transduction of other signals such as phytochrome and ABA. Studies of GA‐regulated gene expression, principally of the α‐amylases of cereal aleurone, have identified core GA‐responsive promoter elements, such as the gibberellin response element (GARE), box‐1 and pyrimidine boxes, as well as elements that may lend specificity to GA‐regulated expression, such as the Opaque‐2‐similar element (O2S), and TRE and CRE motifs. One of the most striking features of all of these studies of the molecular basis of GA action is the interaction of GA‐dependent regulatory elements with those of other factors such as ABA. GA‐response elements also appear to be conserved between disparate GA‐response systems. For example, Myb transcription factors appear to regulate a multitude of GA‐induced genes in cereal aleurone as well as to alter GA responses when expressed in Arabidopsis. Thus the study of GA signal transduction and response systems is highlighting the conservation of regulatory elements used by plants. These common factors, used by distinct signal transduction systems, provide a molecular basis for the integration of the GA signal with other growth regulators that is the hallmark of plant growth and development.

Influence of pH and plant growth regulators on secondary metabolite production and antioxidant activity of Stevia rebaudiana (Bert)

“…The authors germinated seeds on GA3 (0.4 mg L -1 ) media at pH 5.8 and obtained 30 and 55% germination values from seeds originated from Paraguay and United States, respectively. Gibberellins promoted seed germination in a number of plant species [21,22], though treatment with cytokinins was also reported to break seed dormancy in some plant species [23,24]. Here, the maximum germination was obtained by combination of GA3 and BA.…”

Gibberellin/Abscisic Acid Antagonism in Barley Aleurone Cells: Site of Action of the Protein Kinase PKABA1 in Relation to Gibberellin Signaling Molecules

“…GAMyb transactivation followed a dosage-dependent pattern (Figure 1), and more importantly, GAMyb-BD, a truncated protein containing only the DNA binding domain of GAMyb, not only failed to transactivate the ␣-amylase promoter but also blocked the GA signal transduction pathway in aleurone layers (Figure 2). We suggest that GAMyb-BD interferes with the binding of the endogenous protein to the GARE sequence, impairing the transcription of the ␣-amylase gene.The role of protein phosphorylation/dephosphorylation in GA/ABA signal transduction in barley aleurone layers has been suggested elsewhere (Bethke et al, 1997;Leung and Giraudat, 1998;Ritchie and Gilroy, 1998b). We have shown previously that constitutive expression of an ABA-inducible protein kinase, PKABA1, strongly suppressed the GA induction of ␣-amylase and proteinase genes .…”

DELLA proteins regulate arbuscule formation in arbuscular mycorrhizal symbiosis

“…This phenotype suggests that the symbiosis-associated link between phosphate and carbon has been uncoupled in this mutant. It is known that GA signaling can have direct effects on starch metabolism (97,98). During AM symbiosis, starch decreases as the roots become colonized (99).…”