Foolish seedlings and DELLA regulators: the functions of rice SLR1 and Arabidopsis RGL1 in GA signal transduction.

As every student of plant biology learns, gibberellin (GA) was first isolated in Japan in the 1930s from a fungus that causes a serious disease in rice, called “foolish seedling disease” ( bakanae-byo ) by Japanese farmers. Afflicted plants were characterized by excessive growth of seedlings and a decline in seed production in mature plants. The purified active compound was named for the fungus, an ascomycete Fusarium species called Gibberella fuikuroi in the sexual stage (Phinney and West, 1959). It was soon discovered that application of GA to certain dwarf varieties of numerous plant species would cause the plants to grow to normal height and sometimes even taller. The reader is referred to Taiz and Zeigler (1991) for a particularly dramatic illustration of the effect of GA on stem elongation. In addition to its role in controlling cell and stem elongation, GA action is essential in various other stages of plant development, including seed germination and flower development. GA responses are regulated through control of the level of bioactive GA via the regulation of GA biosynthesis and catabolism (deactivation) and through transduction and perception of the active GA signal to various locations throughout the plant. Cell elongation is known to be affected by other hormones and signaling molecules, including cytokinin, ethylene, brassinosteroid, Ca 2 , and sugars, but most of these effects ultimately may result from how these molecules impinge upon the biosynthesis, signal transduction, and/or perception of GA.