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. 2021 Jan 5;185(3):663–681. doi: 10.1093/plphys/kiaa082

Figure 6.

Figure 6

Possible scenarios for the function of nanoclustering in ROP signaling. Note that most of these scenarios have not been formally demonstrated and they remain to be explored. In addition, these scenarios are not mutually exclusive and not exhaustive. A, Nanodomains appear to spatially segregate active (GDP-loaded) and inactive (GTP-loaded) ROPs. However, only a portion (∼30% to 40%) of activated ROPs are localized in nanodomains and this model does not explain by itself why nanodomains are required for downstream signaling. B, Nanodomains could be a favorable membrane environment for ROPs to meet with their effectors, explaining the requirement for nanodomains in signaling. C, ROPs may also recruit their effectors specifically in nanodomains to induce signaling. D, Nanodomains may act as signaling platforms to trigger specific output, as seen in response to auxin treatments or osmotic stress (Platre, 2019; Smokvarska, 2020). E, It is possible that ROP nanodomain formation allows the clustering of downstream effectors, which could induce low energy interactions between them. Such multivalent interaction therefore explains the requirement for nanoclustering in signaling. F, It is possible that multiple ROPs cluster within the same nanodomains, thereby scaffolding several ROP effectors required for signaling. G, It is also possible that multiple ROPs localize to different nanodomains, which could ensure the propagation of specific cytosolic outputs. H, The stabilization of ROPs in nanodomains could increase their dwell time at the plasma membrane, which may be required to stabilize their effector at the cell surface and/or allow them sufficient time to catalyze their reaction. I, The clustering of ROPs in nanodomains may induce the formation of phase-separated cytosolic condensates below the plasma membrane, which could be required for effector function. J, The clustering of ROPs in nanodomains may quantitatively control the strength of the output signal even when the input signal is constant. According to this model, variation in membrane lipids could act like a rheostat that tunes the signaling capacity of cells. Such a model has been proposed for the membrane lipid phosphatidylserine during the ROP6 response to auxin (Platre et al., 2019). PM, plasma membrane, ND, nanodomain. Effectors are represented as a U-shaped protein.