Key Laboratory of Molecular Design for Plant Cell Factory of Guangdong Higher Education Institutes, Institute of Plant and Food Science, Department of Biology, School of Life Sciences, Southern University of Science and Technology, Shenzhen 518055, China.
National Center for Transgenic Research in Plants, Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
Plant Cell. 2023 Sep 1;35(9):3485-3503. doi: 10.1093/plcell/koad170.
Ambient light and the endogenous circadian clock play key roles in regulating Arabidopsis (Arabidopsis thaliana) seedling photomorphogenesis. PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) acts downstream of both light and the circadian clock to promote hypocotyl elongation. Several members of the R2R3-MYB transcription factor (TF) family, the most common type of MYB TF family in Arabidopsis, have been shown to be involved in regulating photomorphogenesis. Nonetheless, whether R2R3-MYB TFs are involved in connecting the light and clock signaling pathways during seedling photomorphogenesis remains unknown. Here, we report that MYB112, a member of the R2R3-MYB family, acts as a negative regulator of seedling photomorphogenesis in Arabidopsis. The light signal promotes the transcription and protein accumulation of MYB112. myb112 mutants exhibit short hypocotyls in both constant light and diurnal cycles. MYB112 physically interacts with PIF4 to enhance the transcription of PIF4 target genes involved in the auxin pathway, including YUCCA8 (YUC8), INDOLE-3-ACETIC ACID INDUCIBLE 19 (IAA19), and IAA29. Furthermore, MYB112 directly binds to the promoter of LUX ARRHYTHMO (LUX), the central component of clock oscillators, to repress its expression mainly in the afternoon and relieve LUX-inhibited expression of PIF4. Genetic evidence confirms that LUX acts downstream of MYB112 in regulating hypocotyl elongation. Thus, the enhanced transcript accumulation and transcriptional activation activity of PIF4 by MYB112 additively promotes the expression of auxin-related genes, thereby increasing auxin synthesis and signaling and fine-tuning hypocotyl growth under diurnal cycles.
环境光和内源性生物钟在调节拟南芥（Arabidopsis thaliana）幼苗光形态建成中发挥着关键作用。PHYTOCHROME-INTERACTING FACTOR 4（PIF4）作为光和生物钟信号的下游因子，促进下胚轴伸长。拟南芥中最常见的 R2R3-MYB 转录因子（TF）家族的几个成员已被证明参与调节光形态建成。然而，R2R3-MYB TFs 是否参与连接幼苗光形态建成过程中的光和时钟信号通路尚不清楚。在这里，我们报告 R2R3-MYB 家族成员 MYB112 作为拟南芥幼苗光形态建成的负调控因子。光信号促进 MYB112 的转录和蛋白积累。myb112 突变体在持续光照和昼夜循环中表现出短下胚轴。MYB112 与 PIF4 物理相互作用，增强 PIF4 靶基因在生长素途径中的转录，包括 YUCCA8（YUC8）、INDOLE-3-ACETIC ACID INDUCIBLE 19（IAA19）和 IAA29。此外，MYB112 直接结合生物钟振荡器核心组件 LUX ARRHYTHMO（LUX）的启动子，抑制其在下午的表达，并缓解 LUX 对 PIF4 表达的抑制。遗传证据证实，LUX 在调节下胚轴伸长中是 MYB112 的下游因子。因此，MYB112 增强了 PIF4 的转录物积累和转录激活活性，从而增加了生长素相关基因的表达，从而在昼夜循环下增加了生长素的合成和信号传递，并精细调节下胚轴的生长。
