B-Bolivia, an allele of the maize b1 gene with variable expression, contains a high copy retrotransposon-related sequence immediately upstream

The maize (Zen mays) b1 gene encodes a transcription factor that regulates the anthocyanin pigment pathway. Of the bl alleles With distinct tissue-spe cific expression, B-Peru and B-Bolivio are the only alleles that confer see d pigmentation. B-Bolivia produces variable and weaker seed expression but darker, more regular plant expression relative to B-Peru. Our experiments d emonstrated that B-Bolivia is not expressed in the seed when transmitted th rough the male. When transmitted through the female the proportion of kerne ls pigmented and the intensity of pigment varied. Molecular characterizatio n of B-Bolivia demonstrated that it shares the first 530 bp of the upstream region with B-Peru, a region sufficient for seed expression. Immediately u pstream of 530 by, B-Bolivia is completely divergent from B-Peru. These seq uences share sequence similarity to retrotransposons. Transient expression assays of various promoter constructs identified a 33-bp region in B-Bolivi a that can account for the reduced aleurone pigment amounts (40%) observed with B-Bolivia relative to B-Peru. Transgenic plants carrying the B-Bolivia promoter proximal region produced pigmented seeds. Similar to native B-Bol ivia, some transgene loci are variably expressed in seeds. In contrast to n ative B-Bolivia, the transgene loci are expressed in seeds tt hen transmitt ed through both the male and female. Some transgenic lines produced pigment in vegetative tissues, but the tissue-specificity was different from B-Bol ivia, suggesting the introduced sequences do not contain the B-Bolivia plan t-specific regulatory sequences. We hypothesize that the chromatin contest of the B-Bolivia allele controls its epigenetic seed expression properties, which could be influenced by the adjacent highly repeated retrotransposon sequence.