Plant roots are sustained through meristem activity at the root tip. Two transcriptional pathways, one mediated by PLETHORAs (PLTs) and the other by SHORTROOT and SCARECROW, play major roles in root meristem development. The role of PLTs during root meristem development requires a concentration gradient, which is not only contributed by posttranslational regulation such as growth dilution and intercellular movement but also likely by a largely unknown fine-tuned transcriptional regulatory mechanism. We report here that Arabidopsis (Arabidopsis thaliana) JANUS positively regulates PLT1 expression in the root meristem by recruiting RNA polymerase II (Pol II) to PLT1 and by interacting with PLT1. JANUS-dependent recruitment of Pol II is inhibited through the competitive binding of JANUS by GRF-INTERACTING FACTOR1 (GIF1)/ANGUSTIFOLIA3, a transcriptional cofactor that negatively regulates PLT1 expression. Finally, GIF1 and JANUS, the antagonistic regulators of PLT1, both depend on Arabidopsis IMPORTIN β4 for their nuclear accumulation. The combination of an importin and its two antagonistic cargos in PLT1 transcription may have logistic benefits in fine-tuning the transcription of PLT1 in root meristem.

植物根系通过根尖的分生组织活动维持。两种转录途径，一种由 PLETHORA (PLT) 介导，另一种由 SHORTROOT 和 SCARECROW 介导，在根分生组织发育中起主要作用。PLT 在根分生组织发育过程中的作用需要浓度梯度，这不仅是由翻译后调节（如生长稀释和细胞间运动）造成的，还可能由很大程度上未知的微调转录调节机制造成。我们在此报告拟南芥 ( Arabidopsis thaliana ) JANUS通过将 RNA 聚合酶 II (Pol II)募集到PLT1来正向调节根分生组织中的PLT1表达并通过与 PLT1 交互。JANUS 依赖的 Pol II 募集通过 GRF 相互作用因子 1 (GIF1)/ANGUSTIFOLIA3（一种负调节PLT1表达的转录辅因子）与 JANUS 的竞争性结合而受到抑制。最后，GIF1 和 JANUS，PLT1 的拮抗调节因子，它们的核积累都依赖于拟南芥 IMPORTIN β4。一个输入蛋白和它的两个对立的货物的组合PLT1转录可能有逻辑的好处在微调的转录PLT1根分生组织。