Cytokinins and ethylene control plant development via sensors from the histidine kinase (HK) family. However, downstream signaling pathways for the key phytohormones are distinct. Here we report that not only cytokinin but also ethylene is able to control root apical meristem (RAM) size through activation of the multistep phosphorelay (MSP) pathway. We found that both cytokinin and ethylene-dependent RAM shortening requires ethylene binding to ETR1 and the HK activity of ETR1. The receiver domain of ETR1 interacts with MSP signaling intermediates acting downstream of cytokinin receptors, further substantiating the role of ETR1 in MSP signaling. We revealed that both cytokinin and ethylene induce the MSP in similar and distinct cell types with ETR1-mediated ethylene signaling controlling MSP output specifically in the root transition zone. We identified members of the MSP pathway specific and common to both hormones and showed that ETR1-regulated ARR3 controls RAM size. ETR1-mediated MSP spatially differs from canonical CTR1/EIN2/EIN3 ethylene signaling and is independent of EIN2, indicating that both pathways can be spatially and functionally separated. Furthermore, we demonstrated that canonical ethylene signaling controls MSP responsiveness to cytokinin specifically in the root transition zone, presumably via regulation of ARR10, one of the positive regulators of MSP signaling in Arabidopsis.

细胞分裂素和乙烯通过组氨酸激酶 (HK) 家族的传感器控制植物发育。然而，关键植物激素的下游信号通路是不同的。在这里，我们报告不仅细胞分裂素而且乙烯能够通过激活多步磷酸层 (MSP) 途径来控制根尖分生组织 (RAM) 的大小。我们发现细胞分裂素和乙烯依赖性 RAM 缩短都需要乙烯与 ETR1 结合和 ETR1 的 HK 活性。ETR1 的接收域与作用于细胞分裂素受体下游的 MSP 信号传导中间体相互作用，进一步证实了 ETR1 在 MSP 信号传导中的作用。我们发现细胞分裂素和乙烯都在相似和不同的细胞类型中诱导 MSP，ETR1 介导的乙烯信号传导控制 MSP 输出，特别是在根过渡区。ARR3控制 RAM 大小。ETR1 介导的 MSP 在空间上不同于经典的 CTR1/EIN2/EIN3 乙烯信号传导，并且独立于 EIN2，表明这两种途径在空间和功能上都可以分离。此外，我们证明了典型的乙烯信号在根过渡区特别控制 MSP 对细胞分裂素的反应，可能是通过调节ARR10 ，ARR10 是拟南芥中 MSP 信号的正调节因子之一。