Data_Sheet_1_SWELLMAP 2, a phyB-Interacting Splicing Factor, Negatively Regulates Seedling Photomorphogenesis in Arabidopsis.docx

Light-triggered transcriptome reprogramming is critical for promoting photomorphogenesis in Arabidopsis seedlings. Nonetheless, recent studies have shed light on the importance of alternative pre-mRNA splicing (AS) in photomorphogenesis. The splicing factors splicing factor for phytochrome signaling (SFPS) and reduced red-light responses in cry1cry2 background1 (RRC1) are involved in the phytochrome B (phyB) signaling pathway and promote photomorphogenesis by controlling pre-mRNA splicing of light- and clock-related genes. However, splicing factors that serve as repressors in phyB signaling pathway remain unreported. Here, we report that the splicing factor SWELLMAP 2 (SMP2) suppresses photomorphogenesis in the light. SMP2 physically interacts with phyB and colocalizes with phyB in photobodies after light exposure. Genetic analyses show that SMP2 antagonizes phyB signaling to promote hypocotyl elongation in the light. The homologs of SMP2 in yeast and human belong to second-step splicing factors required for proper selection of the 3' splice site (3'SS) of an intron. Notably, SMP2 reduces the abundance of the functional REVEILLE 8 a (RVE8a) form, probably by determining the 3'SS, and thereby inhibits RVE8-mediated transcriptional activation of clock genes containing evening elements (EE). Finally, SMP2-mediated reduction of functional RVE8 isoform promotes phytochrome interacting factor 4 (PIF4) expression to fine-tune hypocotyl elongation in the light. Taken together, our data unveil a phyB-interacting splicing factor that negatively regulates photomorphogenesis, providing additional information for further mechanistic investigations regarding phyB-controlled AS of light- and clock-related genes.

光触发的转录组重编程对于促进拟南芥幼苗的光形态建成至关重要。然而，近期的研究揭示了在光形态建成中，选择性剪接（AS）的替代机制的重要性。剪接因子植物色素信号剪接因子（SFPS）和减少红光响应在cry1cry2背景1（RRC1）中的作用涉及植物色素B（phyB）信号通路，并通过调控光和时钟相关基因的前体mRNA剪接来促进光形态建成。然而，作为phyB信号通路中抑制剂的剪接因子尚未有报道。在本研究中，我们报道了剪接因子SWELLMAP 2（SMP2）在光照下抑制光形态建成。SMP2与phyB在光暴露后通过物理相互作用并在光体内共定位。遗传分析表明，SMP2通过拮抗phyB信号通路来促进光照下的下胚轴伸长。SMP2在酵母和人类中的同源物属于第二步骤剪接因子，这些因子对于内含子3'剪接位点（3'SS）的正确选择是必需的。值得注意的是，SMP2通过确定3'SS，减少了功能性的REVEILLE 8 a（RVE8a）形式，从而抑制了RVE8介导的含有夜间元素（EE）的时钟基因的转录激活。最终，SMP2介导的功能性RVE8等位基因的减少促进了植物色素相互作用因子4（PIF4）的表达，以精细调节光照下的下胚轴伸长。综合来看，我们的数据揭示了一个与phyB相互作用的剪接因子，该因子负向调控光形态建成，为关于phyB控制的光和时钟相关基因的选择性剪接的机制研究提供了额外的信息。