The gibberellins (GAs) are a large family of tetracyclic diterpenoid plant growth substances which are associated with various plant growth and development processes such as seed germination, stem and hypocotyl elongation, leaf expansion, floral initiation, floral organ development, fruit development, and induction of some hydrolytic enzymes in the aleurone of cereal grains. Many GA-related mutants have been identified from plant species, and can be categorized as either GA-sensitive or GAinsensitive. GA-sensitive mutants respond to exogenous GA treatment to rescue their abnormal phenotypes. These kinds of mutations are usually caused by deficiencies in the genes encoding GA catalytic enzymes. Many genes encoding GA-catalytic enzymes have been identified using GA-sensitive mutants, enabling researchers to build a detailed picture of the GA biosynthesis process. By contrast, GA-insensitive mutants do not respond to exogenous GA treatment. The mechanism by which GA triggers signal transduction is currently poorly understood compared with the GA biosynthesis mechanism, but recent progress in molecular genetics and molecular biology have led to the identification of several important genes involved in the GA signaling pathway. These latest advances in understanding this pathway are reviewed in this thematic issue of Journal of Plant Growth Regulation. The eight articles in this issue have been arranged in logical order, from the perception of the extracellular GA signal to the transcription of GA-regulated genes. In making this arrangement, I wanted to start with an article on the GA receptor, but this was not possible because there is currently no clear information about the GA receptor, even though efforts have been made to isolate the GA receptor protein. It has previously been considered that there are two types of GA receptors in plant cells: (1) a plasma membrane-bound receptor that has been primarily studied for its role in the induction of aamylase into the aleurone cells of cereal grains; (2) a cytoplasm-type receptor that has been considered to be mainly involved in shoot elongation. Candidate proteins that can interact with GA (GA-binding protein) have successfully been isolated, but these have not been identified as receptors. Molecular genetics offers another possible approach. When a GA-receptor loses its function, the plant should exhibit a recessive GA-insensitive phenotype. However, such a loss-of-function mutant has not been reported, suggesting that they might be difficult to obtain because GA receptors may present themselves in a redundant manner, as is the case for ethylene receptors. Irrespective of these considerations, the isolation and characterization of the GA receptor(s) is one of the most important targets in this research area. The a subunit of the heterotrimeric G protein (Ga) should be located as a neighboring factor to the membrane-bound GA receptor, as is the case in the Received: 8 April 2003; accepted: 8 April 2003; Online publication: 4 September 2003 *Corresponding author; e-mail: makoto@nuagr1.agr.nagoya-u.ac.jp J Plant Growth Regul (2003) 22:123–125 DOI: 10.1007/s00344-003-0039-2