CLONING AND CHARACTERIZATION OF THE MAIZE AN1 GENE

The Anther ear1 (An1) gene product is involved in the synthesis of ent -kaurene, the first tetracyclic intermediate in the gibberellin (GA) b iosynthetic pathway. Mutations causing the loss of An1 function result in a GA-responsive phenotype that includes reduced plant height, dela yed maturity, and development of perfect flowers on normally pistillat e ears, The an1::Mu2 891339 allele was recovered from a Mutator (Mu) F -2 family. Using Mu elements as molecular probes, an An1-containing re striction fragment was identified and cloned. The identity of the clon ed gene as An1 was confirmed by using a reverse genetics screen for ma ize families that contain a Mu element inserted into the cloned gene a nd then by demonstrating that the insertion causes an an1 phenotype. T he predicted amino acid sequence of the An1 cDNA shares homology with plant cyclases and contains a basic N-terminal sequence that may targe t the An1 gene product to the chloroplast. The sequence is consistent with the predicted subcellular localization of AN1 in the chloroplast and with its biochemical role in the cyclization of geranylgeranyl pyr ophosphate, a 20-carbon isoprenoid, to ent-kaurene. The semidwarfed st ature of an1 mutants is in contrast with the more severely dwarfed sta ture of GA-responsive mutants at other loci in maize and may be caused by redundancy in this step of the GA biosynthetic pathway. DNA gel bl ot analysis indicated that An1 is a single-copy gene that lies entirel y within the deletion of the an1-bz2-6923 mutant. However, homozygous deletion mutants accumulated ent-kaurene to 20% of the wild-type level , suggesting that the function of An1 is supplemented by an additional activity.