A bHLH regulatory gene in the common morning glory, Ipomoea purpurea, controls anthocyanin biosynthesis in flowers, proanthocyanidin and phytomelanin pigmentation in seeds, and seed trichome formation
A bHLH regulatory gene in the common morning glory, Ipomoea purpurea, controls anthocyanin biosynthesis in flowers, proanthocyanidin and phytomelanin pigmentation in seeds, and seed trichome formation
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DOI：
10.1111/j.1365-313x.2006.02988.x
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发表时间：
2007-02-01
期刊：
影响因子：
7.2
通讯作者：
Iida, Shigeru
中科院分区：
文献类型：
--
作者：
Park, Kyeung-Il;Ishikawa, Naoko;Iida, Shigeru
花青素着色的转录调控蛋白包括含有R2R3-MYB结构域、bHLH域和保守的WD40重复序列的蛋白质，它们之间的相互作用决定了要表达的基因集。紫菜的自发象牙种子(IVs)突变体表现出浅色的花朵和象牙种子，是由DNA转座子插入到编码bHLH转录调控因子的bHLH2基因中引起的。在这些IVs突变体的幼嫩花蕾中，观察到编码花青素生物合成酶的所有结构基因的表达部分减少。在IVS种皮中，DFR-B和ANS转录本完全被取消，而黄酮醇生物合成的早期生物合成基因仍然活跃。原花青素和植物黑素色素在象牙种皮中的产生和积累都显著减少。此外，象牙种子中未分枝的毛状体比野生型深棕色种子的更小，数量更少，并且由于突出的切向壁，深棕色种子中没有毛状体的表皮表面看起来比象牙种子的更粗糙。虽然紫花菊bHLH2基因与矮牵牛AN1基因的亲缘关系最近，已知该基因突变会产生白色的花，但突变体的表皮花枝中的液泡碱化似乎是正常的。这些结果从转录调控因子控制花和种子色素形成的功能以及其他表皮特征方面进行了讨论。
The transcriptional regulators for anthocyanin pigmentation include proteins containing R2R3-MYB domains, bHLH domains and conserved WD40 repeats, and their interactions determine the set of genes to be expressed. Spontaneous ivory seed (ivs) mutants of Ipomoea purpurea displaying pale pigmented flowers and ivory seeds are caused by insertions of DNA transposons into the bHLH2 gene that encodes a bHLH transcriptional regulator. A partial reduction in the expression of all structural genes encoding enzymes for anthocyanin biosynthesis was observed in the young flower buds of these ivs mutants. The DFR-B and ANS transcripts were completely abolished in the ivs seed coats, whereas the early biosynthetic genes for flavonol biosynthesis remained active. The production and accumulation of both proanthocyanidin and phytomelanin pigments in the ivory seed coats were drastically reduced. Moreover, the unbranched trichomes in the ivory seeds were smaller in size and fewer in number than those in the wild-type dark-brown seeds, and the surface of the epidermis without trichomes in the dark-brown seeds looked rougher, due to the protruding tangential walls, than that in the ivory seeds. Although the I. purpurea bHLH2 gene is the most closely related to the petunia AN1 gene, whose mutation is known to confer white flowers and to be deficient in acidification of their vacuoles, the vacuolar alkalization in the epidermal flower limbs of I. purpurea ivs mutants appears to occur normally. These results are discussed with regard to the function of bHLH transcriptional regulators controlling flower and seed pigmentation as well as other epidermal traits.