Tansley Review No. 100 - Gibberellins: regulating genes and germination

The range of processes regulated by gibberellins (GAs) covers all aspects o f the life history of the plant from seed germination to vegetative growth and flowering. In seeds there has been an intensive search, using the techn iques of both biochemistry and cell biology, for the regulatory molecules l inking GA perception to gene regulation and the events of germination. Alth ough a GA receptor has yet to be identified, the site of perception has bee n localized to the plasma membrane. Calmodulin, Ca2+ and cGMP have also bee n identified as elements of the GA signal transduction pathway. These regul ators parallel many of the signalling elements identified in the transducti on of other signals such as phytochrome and ABA. Studies of GA;regulated ge ne expression, principally of the alpha-amylases of cereal aleurone, have i dentified core GA-responsive promoter elements, such as the gibberellin res ponse element (GARE), box-1 and pyrimidine boxes, as well as elements that may lend specificity to GA-regulated expression, such as the Opaque-2-simil ar 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 interac tion of GA-dependent regulatory elements with those of other factors such a s ABA. GA-response elements also appear to be conserved between disparate G A-response systems. For example, Myb transcription factors appear to regula te a multitude of GA-induced genes in cereal aleurone as well as to alter G A responses when expressed in Arabidopsis. Thus the study of CA signal tran sduction and response systems is highlighting the conservation of regulator y elements used by plants. These common factors, used by distinct signal tr ansduction systems, provide a molecular basis for the integration of the GA signal with other growth regulators that is the hallmark of plant growth a nd development.