Transposon Tagging and Molecular Analysis of the Maize Regulatory Locus opaque-2

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Abstract
Genetic analyses suggested that the opaque-2 ( o2 ) locus in maize acts as a positive, transacting, transcriptional activator of the zein seed storage-protein genes. Because isolation of the gene is requisite to understanding the molecular details of this regulation, transposon mutagenesis with the transposable element suppressor-mutator ( Spm ) was carried out, and three mutable o2 alleles were obtained. One of these alleles contained an 8.3-kilobase autonomous Spm , another a 6.8-kilobase nonautonomous Spm , and the third an unidentified transposon that is unrelated to Spm . A DNA sequence flanking the autonomous Spm insertion was verified to be o2 -specific and provided a probe to clone a wild-type allele. Northern blots indicated that the gene is expressed in wild-type endosperm but not in leaf tissues or in endosperms homozygous for a mutant allele of the O2 gene. A transcript was detected in endosperms homozygous for mutations at opaque-7 and floury-2 , an indication that O2 expression is independent of these two other putative regulators of zein synthesis.