TRANSPOSON SEQUENCES DRIVE TISSUE-SPECIFIC EXPRESSION OF THE MAIZE REGULATORY GENE R-S

The R family of genes in maize encodes transcription factors that acti vate anthocyanin synthesis. The R-r complex at the r locus contains tw o components, of which one, the aleurone-pigmenting R-s subcomplex, is an unusual promoter flanked by two head-to-head, nearly identical cod ing regions. The central region of the promoter, designated sigma(r) c ontains inverted terminal repeats and subterminal repeats, both of whi ch are features of the CACTA transposon family. Transcription from the R-s promoter was strongest in aleurone but transcripts had a surprisi ngly variable initiation site and splicing pattern. Microprojectile bo mbardment indicated that the sequences introduced by transposition act as an enhancer of transcription in aleurone but not in coleoptile or mesocotyl tissue. Moreover, the region containing the subterminal repe ats was able to activate expression when fused to a minimal promoter, suggesting that a factor that binds to the repeats may be responsible. Regions downstream of sigma encode a leader containing three ORFs, tw o of which are variably removed by splicing. The results presented her e show that transposons can mediate the rearrangement of genes and con fer new splicing and expression patterns. In the case of the r complex , this has resulted in a new phenotype, the pigmentation of aleurone c ells.