During the summer of 1997, two research groups succeeded in bringing closure to a classic tale in genetics. After 131 years, they identified one of Mendel's pea genes at the molecular level. The gene, called Le, controls stem length--plants with defective copies are shorter than normal. Characterized in both pea and Arabidopsis, the gene encodes an enzyme called gibberellin 3b-hydroxylase, which converts two precursors of the growth regulator gibberellin into active forms, including gibberellin 1.1,2 Le was the second of Mendel's genes to be identified. Re-searchers pulled out the first--for a starch-branching enzyme that in defective form causes the wrinkled seed trait--12 years ago.3
Now a gene called GA20ox-2 encoding another enzyme in the gibberellin biosynthetic pathway has been conquered, this time in rice.4 The enzyme is GA20 oxidase, which catalyzes three steps in the pathway leading to production of gibberellin 20, a substrate for the b- hydroxylase. Four alleles ...
