Divergence in homoeolog expression of the grain length-associated gene GASR7 during wheat allohexaploidization
Divergence in homoeolog expression of the grain length-associated gene GASR7 during wheat allohexaploidization
复制标题
DOI：
10.1016/j.cj.2014.08.005
复制
发表时间：
2015-02
期刊：
影响因子：
6.6
通讯作者：
Dongdong Zhang;Wang Bingnan;Jun-Peng Zhao;Xu-han-hui Zhao;Lianquan Zhang;Dengcai Liu;Lingli Dong
中科院分区：
文献类型：
--
作者：
Dongdong Zhang;Wang Bingnan;Jun-Peng Zhao;Xu-han-hui Zhao;Lianquan Zhang;Dengcai Liu;Lingli Dong
六倍体小麦的大部分基因位于亚基因组 A、B 和 D 中，具有三倍同源性。GASR7 是 Snakin/GASA 基因家族的成员，与小麦粒长发育有关。然而，对其同源基因在小麦多倍体中表达的差异知之甚少。我们研究了合成六倍体小麦品系中未成熟种子中 GASR7 同源物的表达模式，该品系的籽粒像其母本 (Triticum turgidum, AABB, PI 94655) 一样细长，而其父本祖先 (Aegilops tauschii, DD, AS2404) 的种子形状为圆形。我们发现GASR7的B同源物是母本四倍体祖代和六倍体后代中该基因总表达水平的主要贡献者，而A和D同源物的表达水平要低得多。为了了解调节不同GASR7同源基因的可能机制，我们首先分析了三个同源基因的启动子序列，发现它们都含有赤霉酸（GA）反应元件，其中TaGASR7B启动子（pTaGASR7B）独特地具有额外的预测转录增强子。这通过对刺突进行 GA 处理得到了证实，其中所有三种同源物均被诱导，对 TaGASR7B 的反应要强得多。 McrBC酶测定表明，pTaGASR7D的甲基化状态在异源六倍体化期间增加，与TaGASR7D的抑制表达一致。对于 pTaGASR7A，发现重复序列衍生的 24 核苷酸 (nt) 小干扰 RNA (siRNA) 的分布，这表明可能的表观遗传调控，因为已知 24 nt siRNA 介导 RNA 依赖性 DNA 甲基化。因此，我们的结果表明遗传和表观遗传机制可能与多倍体小麦中 GASR7 同源表达的差异有关。
Hexaploid wheat has triplicated homoeologs for most of the genes that are located in subgenomes A, B, and D.GASR7, a member of the Snakin/GASA gene family, has been associated with grain length development in wheat. However, little is known about divergence of its homoeolog expression in wheat polyploids. We studied the expression patterns of theGASR7homoeologs in immature seeds in a synthetic hexaploid wheat line whose kernels are slender like those of its maternal parent (Triticum turgidum, AABB, PI 94655) in contrast to the round seed shape of its paternal progenitor (Aegilops tauschii, DD, AS2404). We found that the B homoeolog ofGASR7was the main contributor to the total expression level of this gene in both the maternal tetraploid progenitor and the hexaploid progeny, whereas the expression levels of the A and D homoeologs were much lower. To understand possible mechanisms regulating differentGASR7homoeologs, we firstly analyzed the promoter sequences of three homoeologous genes and found that all of them contained gibberellic acid (GA) response elements, with theTaGASR7Bpromoter (pTaGASR7B) uniquely characterized by an additional predicted transcriptional enhancer. This was confirmed by the GA treatment of spikes where all three homoeologs were induced, with a much stronger response forTaGASR7B. McrBC enzyme assays showed that the methylation status at pTaGASR7Dwas increased during allohexaploidization, consistent with the repressed expression ofTaGASR7D. For pTaGASR7A, the distribution of repetitive sequence-derived 24-nucleotide (nt) small interfering RNAs (siRNAs) were found which suggests possible epigenetic regulation because 24-nt siRNAs are known to mediate RNA-dependent DNA methylation. Our results thus indicate that both genetic and epigenetic mechanisms may be involved in the divergence ofGASR7homoeolog expression in polyploid wheat.