An intragenic tandem duplication in a transcriptional regulatory gene for anthocyanin biosynthesis confers pale-colored flowers and seeds with fine spots in Ipomoea tricolor
An intragenic tandem duplication in a transcriptional regulatory gene for anthocyanin biosynthesis confers pale-colored flowers and seeds with fine spots in Ipomoea tricolor
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DOI：
10.1111/j.1365-313x.2004.02098.x
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发表时间：
2004-06-01
期刊：
影响因子：
7.2
通讯作者：
Iida, S
中科院分区：
文献类型：
--
作者：
Park, KI;Choi, JD;Iida, S
野生型牵牛花(Ipomoea Tricolor)开出亮蓝色的花，种子呈深棕色，而其自发突变体蓝星(Blue Star)携带可变的象牙种子杂色(IVS-v)等位基因，开出淡蓝色的花，有几个细小的蓝色斑点，象牙种子有微小的深褐色斑点。该突变等位基因是由一个含有基本螺旋-环-螺旋(BHLH)DNA结合基序的转录激活因子基因内3.3kbp的串联重复引起的。每个串联重复序列两侧都有一个3bP的序列AAT，这表明3bp微同源性被用来产生串联复制。该突变体的淡蓝色花蕾中的转录本包含一个583个碱基的内部串联复制，导致产生一个缺失bHLH域的截短多肽。该突变体花蕾中大多数花青素生物合成酶结构基因的mRNA积累量显著减少。与野生型转录激活子mRNAs相同的转录本大量存在于斑驳花的蓝色斑点中，而含有583个碱基串联重复的转录本在同一花的淡蓝色背景中占主导地位。这里研究的花和种子的花色很可能是由于编码花青素生物合成的bHLH转录激活子的基因的基因内串联复制之间的体细胞同源重组造成的，而各种花的花色可能是由于切除插入到色素形成基因中的DNA转座子而引起的。
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.