Mol Plant|兰州大学黎家团队揭示RGF1-RGI1一种肽-受体复合物，通过MAPK信号级联调节拟南芥根分生组织的发育。

根的生长是通过顶端分生组织中细胞的持续分裂来维持的。根分生组织生长因子1(RGF1)是一种调节根干细胞生态位维持的重要多肽激素。以往的研究发现，5个密切相关的富含亮氨酸重复序列的受体样蛋白激酶(LRRRLKs)被命名为Rgf1受体(Rgf1 INSENSITIVES，RGIS)或Rgf1受体(RGFRs)，它们能够感知Rgf1信号并冗余地控制根干细胞生态位的维持。

RGF1主要通过两个下游转录因子Plethora1(PLT1)和PLT2来调节根分生组织的活性。然而，连接细胞表面RGF1-RGI1和细胞核PLT的调节蛋白并未被鉴定。在此，我们报道了Rgf1处理拟南芥幼苗后，

丝裂原活化蛋白激酶4(MKK4)和MAP激酶3(MPK3)与RGI1-FLAG共沉淀。遗传和生化分析证实，MKK4和MKK5及其下游靶标MPK3和MPK6是根分生组织发育所必需的RGI依赖性调控因子。

此外，我们还发现MKK4/MKK5-MPK3/MPK6模块在MAPKKK基因YDA下游发挥功能。我们的结果表明，Rgf1-RGI1通过YDA-MKK4/MKK5-MPK3/MPK6信号级联调控PLT1/PLT2的表达。

Root growth is maintained by the continuous division of cells in the apical meristem. ROOT MERISTEM GROWTH FACTOR 1 (RGF1) is a critical peptide hormone regulating root stem cell niche maintenance. Previous studies discovered that five closely related leucine-rich repeat receptor-like protein kinases (LRRRLKs), named RGF1 INSENSITIVES (RGIs) or RGF1 RECEPTORS (RGFRs), are able to perceive the RGF1 signal and redundantly control root stem cell niche maintenance. RGF1 regulates root meristem activity mainly via two downstream transcription factors, PLETHORA 1 (PLT1) and PLT2. Regulatory proteins connecting cell surface RGF1-RGI1 and nuclear PLTs, however, were not identified. Here, we report that the mitogen-activated protein (MAP) kinase kinase 4 (MKK4) and MAP kinase 3 (MPK3) were coimmunoprecipitated with RGI1-FLAG after Arabidopsis seedlings were treated with RGF1. Genetic and biochemical assays confirmed that MKK4 and MKK5, and their downstream targets MPK3 and MPK6, are essential RGI-dependent regulators of root meristem development. In addition, we found that the MKK4/MKK5-MPK3/MPK6 module functions downstream of YDA, a MAPKKK. Our results demonstrate that RGF1-RGI1 regulate the expression of PLT1/PLT2 via a YDA-MKK4/MKK5-MPK3/MPK6 signaling cascade.

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