B-Bolivia, an Allele of the Maize b1 Gene with Variable Expression, Contains a High Copy Retrotransposon-Related Sequence Immediately Upstream

• Published in: Plant physiology (Bethesda) Vol. 125; no. 3; pp. 1363 - 1379
• Main Authors: Selinger, David A., Chandler, Vicki L.
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Physiologists 01.03.2001
• Subjects: Ab1 gene; Agronomy. Soil science and plant productions; Alleles; anthocyanin; b1 gene; Biological and medical sciences; Classical and quantitative genetics. Population genetics. Molecular genetics; Corn; Fundamental and applied biological sciences. Psychology; Gene expression; Generalities. Genetics. Plant material; Genes, Plant; Genetics and breeding of economic plants; Genetics, Molecular Biology, and Gene Expression; Molecular and cellular biology; Molecular genetics; Molecular Sequence Data; Phylogeny; Pigmentation; Pigmentation - genetics; Pigments; Plants; Plants, Genetically Modified - genetics; Promoter regions; Promoter Regions, Genetic; Retroelements; Retrotransposons; Seeds; Transgenes; Transgenic animals; Zea mays; Zea mays - genetics; Anthocyanin; Retrotransposon; Monocotyledones; Aleurone; Zea mays; Tissue specificity; Biosynthesis; Metabolic pathway; Gene expression; Structure gene; Cereal crop; Characterization; Allele; Gramineae; Angiospermae; Pigments; Spermatophyta; Intraspecific comparison; Transcription factor
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.125.3.1363

The maize (Zea mays) b1 gene encodes a transcription factor that regulates the anthocyanin pigment pathway. Of the b1 alleles with distinct tissue-specific expression, B-Peru and B-Bolivia are the only alleles that confer seed pigmentation. B-Bolivia produces variable and weaker seed expression but darker, more regular plant expression relative to B-Peru. Our experiments demonstrated that B-Bolivia is not expressed in the seed when transmitted through the male. When transmitted through the female the proportion of kernels pigmented and the intensity of pigment varied. Molecular characterization 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 upstream of 530 bp, B-Bolivia is completely divergent from B-Peru. These sequences share sequence similarity to retrotransposons. Transient expression assays of various promoter constructs identified a 33-bp region in B-Bolivia 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-Bolivia, some transgene loci are variably expressed in seeds. In contrast to native B-Bolivia, the transgene loci are expressed in seeds when transmitted through both the male and female. Some transgenic lines produced pigment in vegetative tissues, but the tissue-specificity was different from B-Bolivia, suggesting the introduced sequences do not contain the B-Bolivia plant-specific regulatory sequences. We hypothesize that the chromatin context of the B-Bolivia allele controls its epigenetic seed expression properties, which could be influenced by the adjacent highly repeated retrotransposon sequence.