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. Author manuscript; available in PMC: 2021 Apr 12.
Published in final edited form as: Mol Plant. 2019 Jun 7;12(10):1338–1352. doi: 10.1016/j.molp.2019.05.012

Figure 7. Model for ETR1-mediated integration of cytokinin and ethylene in the control of RAM size.

Figure 7.

Cytokinin activates the MSP signaling pathway in the root stele and upregulates ethylene biosynthesis, creating ethylene that is recognized by ethylene receptors, preferentially by ETR1 and possible participation of ERS1. ETR1 interacts with AHP proteins and contributes to the MSP output via phosphorylation of ARRs-B including ARR10 that target individual ARRs-A, particularly ARR3. The ability of ETR1 to bind ethylene and ETR1 HK activity are necessary for the ethylene-dependent control of MSP output that integrates both cytokinin and ethylene signals in the control of cell differentiation. EIN2-mediated canonical ethylene signaling controls MSP sensitivity to cytokinins in the root TZ via upregulating the amount of phosphorylatable ARR10. However, the direct control of cell differentiation via canonical ethylene signaling (grey dashed arrows and grey characters) in parallel to MSP also cannot be excluded. Green colored rectangle corresponds to stele cells and yellow to epidermis in the root TZ. Green arrows depict cytokinin-specific regulation, the orange arrows represent ethylene-mediated control of the MSP DZ, differentiation zone; TZ, transition zone; RAM, root apical meristem.