Huang Zong-An, Zhao Ting, Wang Ning, Zheng Shu-Song
State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, West Beichen Road 1, Chaoyang District, Beijing, 100101, China.
Institute of Vegetable Sciences, Wenzhou Academy of Agricultural Sciences, Wenzhou Vocational College of Science and Technology, Wenzhou, 325014, China.
Bot Stud. 2016 Dec;57(1):24. doi: 10.1186/s40529-016-0138-6. Epub 2016 Sep 8.
Anthocyanins are the conspicuous pigments of flowering plants and participate in several aspects of plant development and defense, such as seeds and pollens dispersal. Leaf colour (Lc) is the first basic/helix-loop-helix (bHLH) transcription factor controlling anthocyanin biosynthesis isolated from maize (Zea mays L.). Ectopic expression of maize Lc enhanced anthocyanin biosynthesis in many plants including tobacco (Nicotiana tobacum L.). However, the molecular regulatory mechanism of anthocyanin biosynthesis in the different floral parts of tobacco remains largely unknown. Therefore, the molecular and biochemical characterization of anthocyanin biosynthesis were investigated in the flowers of both wild type and Lc-transgenic tobacco plants.
At the reproductive stage, with respect to the different parts of the flowers in wild type SR1, the calyxes and the pistils were green, and the petals and the filaments showed light pink pigmentation; the Lc-transgenic tobacco exhibited light red in calyxes and crimson in petals and in filaments respectively. Correspondingly, the total anthocyanin contents (TAC) in calyxes, petals and filaments of Lc-transgenic plants were much higher than that of the counterparts in SR1. Though the TAC in anthers of Lc-transgenic plants was low, it was still significantly higher than that of SR1. SR1 has almost the same TAC in the pistils as Lc-transgenic plants. Consistent with the intense phenotype and the increased TAC, Lc was weakly expressed in the calyxes and strongly expressed in petals and filaments of Lc-transgenic plants, while Lc was not detected in SR1. The expression level of NtAN2 in petals was similar between SR1 and Lc-transgenic lines. In agreement with the expression profile of Lc, both early (NtCHS) and late anthocyanin-biosynthetic genes (NtDFR, NtF3'H, and NtANS) were coordinately up-regulated in the counterparts of flowers. HPLC analysis demonstrated that the cyanidin (Cya) deposition was mainly responsible for the intense pigmentation of Lc-transgenic tobacco.
Ectopic expression of Lc greatly enhanced both early- and late- anthocyanin-biosynthetic gene expression, and therefore resulted in the Cya-based TAC increase in the calyxes, the filaments and the petals in tobacco plants.
花青素是开花植物中显著的色素，参与植物发育和防御的多个方面，如种子和花粉传播。叶色（Lc）是从玉米（Zea mays L.）中分离得到的第一个控制花青素生物合成的基本/螺旋-环-螺旋（bHLH）转录因子。玉米Lc的异位表达增强了包括烟草（Nicotiana tobacum L.）在内的许多植物中的花青素生物合成。然而，烟草不同花器官中花青素生物合成的分子调控机制仍 largely未知。因此，对野生型和Lc转基因烟草植株花中的花青素生物合成进行了分子和生化特征研究。
在生殖阶段，对于野生型SR1花的不同部分，花萼和雌蕊为绿色，花瓣和花丝呈现浅粉色色素沉着；Lc转基因烟草的花萼呈浅红色，花瓣和花丝分别呈深红色。相应地，Lc转基因植株花萼、花瓣和花丝中的总花青素含量（TAC）远高于SR1中的对应部分。虽然Lc转基因植株花药中的TAC较低，但仍显著高于SR1。SR1雌蕊中的TAC与Lc转基因植株几乎相同。与强烈的表型和增加的TAC一致，Lc在Lc转基因植株的花萼中弱表达，在花瓣和花丝中强表达，而在SR1中未检测到Lc。SR1和Lc转基因株系花瓣中NtAN2的表达水平相似。与Lc的表达谱一致，花青素生物合成的早期（NtCHS）和晚期基因（NtDFR、NtF3'H和NtANS）在花的对应部分均协同上调。高效液相色谱分析表明，矢车菊素（Cya）的沉积是Lc转基因烟草强烈色素沉着的主要原因。
Lc的异位表达极大地增强了花青素生物合成早期和晚期基因的表达，因此导致烟草植株花萼、花丝和花瓣中基于Cya的TAC增加。
