Physiological genetics of the dominant gibberellin-nonresponsive maize dwarfs,Dwarf8 and Dwarf9

Maize (Zea mays L.) Dwarf8-1 (D8-1) is an andromonoecious dwarf mutant proposed to be involved in gibberellin (GA) reception (Fujioka et al. 1988b; Harberd and Freeling 1989). The mutant D8-1 is dominant and GA-nonresponsive (Phinney 1956). We show by map position and similarity of phenotype that five additional dwarf mutants are D8 alleles. We show by map position and similarity of phenotype that a second andromonoecious dwarf mutant, D9-1, defines a duplicate gene. Maize D9-1 and each dominant D8 allele specify a different plant stature, from very mild to very severe dwarfism. Plants of D9-1 and all dominant D8 alleles, except D8-1591, were GA-nonresponsive when treated with 7500 nmol GA₃. The behavior of the mild dwarf D8-1591 was unique in that a small but significant growth response was detected (37% for D8-1591 vs. 130% for the wild type) when treated with 7500 nmol GA₃. These results establish that all dwarf genotypes, except D8-1591, in one dose set a maximum limit on plant growth and block the normal response to GA. When treated with the GA-synthesis inhibitor paclobutrazol, plants of all dwarf genotypes and wild-type siblings were severely dwarfed. Plants of all dwarf genotypes treated with the GA-synthesis inhibitor paclobutrazol and GA₃ were returned to their normal dwarf phenotype. Dominant dwarfing, delayed flowering, increased tillering, and anther development in the ear are characteristic features of D9-1 and all D8 alleles. The GA-synthesis-deficient dwarfs also have these characteristic features. We discuss the function of the wild-type gene product in the context of the observed results.Abbreviations D8 Dwarf8 - D9 Dwarf9 - GA_(n) gibberellin A_(n) - GA₃ gibberellic acid - MNL Maize Genetics Cooperation Newsletter - NIL near-isogenic lines - RFLP restriction fragment length polymorphism - WT wild type This work was supported, in part, by a National Science Foundation Plant Postdoctoral Fellowship to R.G.W., by grants from NIH and ICI Seeds to M.F., the NSF Center for Plant Developmental Biology and the California Agriculture Experiment Station. Much of the work was done in the laboratory of Tim Helentjaris and was supported by a grant from Pioneer Hi-Bred Int'l. The generous gifts of the dominant dwarfing mutants from M.G. Neuffer and O.E. Nelson Jr. are gratefully acknowledged.