intragenic tandem duplication in a transcriptional regulatory gene for anthocyanin biosynthesis confers pale-colored flowers and seeds with fine spots in Ipomoea tricolor

• Published in: The Plant journal : for cell and molecular biology Vol. 38; no. 5; pp. 840 - 849
• Main Authors: Park, K.I, Choi, J.D, Hoshino, A, Morita, Y, Iida, S
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science, Ltd 01.06.2004; Blackwell Science
• Subjects: alleles; anthocyanins; Anthocyanins - biosynthesis; Base Sequence; bHLH protein; bioaccumulation; biochemical pathways; Biological and medical sciences; biosynthesis; Cloning, Molecular; color; DNA Transposable Elements; DNA, Plant - genetics; DNA-binding proteins; enzymes; flower and seed pigmentation; flowers; Flowers - genetics; Fundamental and applied biological sciences. Psychology; gene duplication; Gene Expression Regulation, Plant - genetics; genetic recombination; genome; Genome, Plant; helix-loop-helix motifs; intrachromosomal homologous recombination; intragenic tandem duplication; Ipomoea - genetics; Ipomoea tricolor; messenger RNA; Metabolism; Molecular Sequence Data; mutable allele; nucleotide sequences; ornamental plants; phenotypic variation; Pigmentation; plant morphology; Plant physiology and development; plant proteins; reverse transcriptase polymerase chain reaction; RNA, Messenger - genetics; RNA, Plant - genetics; seeds; Seeds - genetics; Seeds - physiology; Storage and secretion, pigments, phytochrome; tandem repeat sequences; transcription factors; Transcription, Genetic - genetics; transcriptional factor; Anthocyanin; Flower; flower and seed pigmentation; Seeds; Transcription; Homologous recombination; Biosynthesis; intragenic tandem duplication; mutable allele; Convolvulaceae; Phenotype; Regulation(control); Gene; Dicotyledones; Angiospermae; Pigments; Spermatophyta; Mutation; transcriptional factor; intrachromosomal homologous recombination; bHLH protein
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/j.1365-313X.2004.02098.x

While the wild-type morning glory (Ipomoea tricolor) displays bright-blue flowers and dark-brown seeds, its spontaneous mutant, Blue Star, carrying the mutable ivory seed-variegated (ivs-v) allele, exhibits pale-blue flowers with a few fine blue spots and ivory seeds with tiny dark-brown spots. The mutable allele is caused by an intragenic tandem duplication of 3.3 kbp within a gene for transcriptional activator containing a basic helix-loop-helix (bHLH) DNA-binding motif. Each of the tandem repeats is flanked by a 3-bp sequence AAT, indicating that the 3-bp microhomology is used to generate the tandem duplication. The transcripts in the pale-blue flower buds of the mutant contain an internal 583-bp tandem duplication that results in the production of a truncated polypeptide lacking the bHLH domain. The mRNA accumulation of most of the structural genes encoding enzymes for anthocyanin biosynthesis in the flower buds of the mutant was significantly reduced. The transcripts identical to the wild-type mRNAs for the transcriptional activator were present abundantly in blue spots of the variegated flowers, whereas the transcripts containing the 583-bp tandem duplication were predominant in the pale-blue background of the same flowers. The flower and seed variegations studied here are likely to be caused by somatic homologous recombination between an intragenic tandem duplication in the gene encoding a bHLH transcriptional activator for anthocyanin biosynthesis, whereas various flower variegations are reported to be caused by excision of DNA transposons inserted into pigmentation genes.