RNA Biology and Molecular Physiology, Faculty of Biology, Bielefeld University, Universit�tsstrasse 25, D-33615 Bielefeld, Germany.
Plant Cell Physiol. 2019 Sep 1;60(9):2040-2050. doi: 10.1093/pcp/pcz124.
The timing of floral initiation is a tightly controlled process in plants. The circadian clock regulated glycine-rich RNA-binding protein (RBP) AtGRP7, a known regulator of splicing, was previously shown to regulate flowering time mainly by affecting the MADS-box repressor FLOWERING LOCUS C (FLC). Loss of AtGRP7 leads to elevated FLC expression and late flowering in the atgrp7-1 mutant. Here, we analyze genetic interactions of AtGRP7 with key regulators of the autonomous and the thermosensory pathway of floral induction. RNA interference- mediated reduction of the level of the paralogous AtGRP8 in atgrp7-1 further delays floral transition compared of with atgrp7-1. AtGRP7 acts in parallel to FCA, FPA and FLK in the branch of the autonomous pathway (AP) comprised of RBPs. It acts in the same branch as FLOWERING LOCUS D, and AtGRP7 loss-of-function mutants show elevated levels of dimethylated lysine 4 of histone H3, a mark for active transcription. In addition to its role in the AP, AtGRP7 acts in the thermosensory pathway of flowering time control by regulating alternative splicing of the floral repressor FLOWERING LOCUS M (FLM). Overexpression of AtGRP7 selectively favors the formation of the repressive isoform FLM-β. Our results suggest that the RBPs AtGRP7 and AtGRP8 influence MADS-Box transcription factors in at least two different pathways of flowering time control. This highlights the importance of RBPs to fine-tune the integration of varying cues into flowering time control and further strengthens the view that the different pathways, although genetically separable, constitute a tightly interwoven network to ensure plant reproductive success under changing environmental conditions.
花的起始时间是植物中一个受到严格控制的过程。生物钟调节甘氨酸丰富的 RNA 结合蛋白（RBP）AtGRP7，它是剪接的已知调节剂，先前被证明主要通过影响 MADS 框抑制物 FLOWERING LOCUS C（FLC）来调节开花时间。AtGRP7 的缺失导致 atgrp7-1 突变体中 FLC 表达升高和开花延迟。在这里，我们分析了 AtGRP7 与自主途径和热感觉途径中花诱导的关键调节剂的遗传相互作用。RNA 干扰介导的 AtGRP8 水平降低在 atgrp7-1 中进一步延迟花转变，与 atgrp7-1 相比。AtGRP7 与 FCA、FPA 和 FLK 在 RBPs 组成的自主途径（AP）分支中起作用。它与 FLOWERING LOCUS D 处于同一分支，AtGRP7 功能丧失突变体显示组蛋白 H3 赖氨酸 4 二甲基化水平升高，这是转录活性的标志。除了在 AP 中的作用外，AtGRP7 通过调节花抑制物 FLOWERING LOCUS M（FLM）的选择性剪接来控制开花时间的热感觉途径。AtGRP7 的过表达选择性有利于抑制型同工型 FLM-β的形成。我们的结果表明，RBP AtGRP7 和 AtGRP8 至少在开花时间控制的两个不同途径中影响 MADS-Box 转录因子。这突出了 RBPs 对微调将不同线索整合到开花时间控制中的重要性，并进一步加强了这样的观点，即不同的途径虽然在遗传上可分离，但构成了一个紧密交织的网络，以确保植物在不断变化的环境条件下生殖成功。
