Graduate School of Agricultural Science, Tohoku University, Aoba-ku, Sendai 980-8572, Japan.
Faculty of Life and Environmental Science, Shimane University, Matsue 690-8504, Japan.
Int J Mol Sci. 2020 Jun 26;21(12):4562. doi: 10.3390/ijms21124562.
To elucidate the molecular mechanism of juvenility and annual flowering of fruit trees, (), an integrator of flowering signals, was investigated in apple as a model. We performed sequence and expression analyses and transgenic experiments related to juvenility with annual flowering to characterize the apple homologs . The phylogenetic tree analysis, which included other MADS-box genes, showed that both MdFLC1 and MdFLC3 belong to the same FLC group. MdFLC1c from one of the splice variants and MdFLC3 contain the four conserved motives of an MIKC-type MADS protein. The mRNA of variants and contain intron sequences, and their deduced amino acid sequences lack K- and C-domains. The expression levels of , , and decreased during the flowering induction period in a seasonal expression pattern in the adult trees, whereas the expression level of did not decrease during that period. This suggests that is involved in flowering induction in the annual growth cycle of adult trees. In apple seedlings, because phase change can be observed in individuals, seedlings can be used for analysis of expression during phase transition. The expression levels of , , and were high during the juvenile phase and low during the transitional and adult phases. Because the expression pattern of suggests that it plays a specific role in juvenility, was subjected to functional analysis by transformation of . The results revealed the function of as a floral repressor. In addition, had CArG box-like sequences, putative targets for the suppression of flowering by MdFLC binding, in the introns and promoter regions. These results indicate that apple homologs of FLC, which might play a role upstream of the flowering signals, could be involved in juvenility as well as in annual flowering. Apples with sufficient genome-related information are useful as a model for studying phenomena unique to woody plants such as juvenility and annual flowering.
为了阐明果树幼年和年开花的分子机制，以苹果为模式，研究了开花信号的整合因子 ()。我们进行了与幼年开花相关的序列和表达分析以及转基因实验，以鉴定苹果的同源物。包括其他 MADS-box 基因在内的系统发育树分析表明，MdFLC1 和 MdFLC3 都属于相同的 FLC 组。MdFLC1c 是一种剪接变体，MdFLC3 含有 MIKC 型 MADS 蛋白的四个保守基序。变体和的 mRNA 含有内含子序列，其推导的氨基酸序列缺乏 K-和 C-结构域。在成年树的季节性表达模式中，和的表达水平在开花诱导期下降，而的表达水平在该时期没有下降。这表明在成年树的年生长周期中，参与了开花诱导。在苹果幼苗中，由于可以观察到个体的阶段变化，因此可以使用幼苗分析在过渡阶段的表达。在幼年阶段，和的表达水平较高，而在过渡和成年阶段则较低。由于的表达模式表明它在幼年阶段发挥特定作用，因此通过转化进行了功能分析。结果表明作为花的阻遏物。此外，在内含子和启动子区域中具有 CArG 盒样序列，可能是 MdFLC 结合抑制开花的靶标。这些结果表明，可能在开花信号的上游发挥作用的苹果 FLC 同源物可能参与幼年和年开花。具有足够基因组相关信息的苹果可用作研究幼年和年开花等木本植物特有现象的模型。
