Figure 9.
Flow diagram suggesting how BIN2 might mediate plant adaptive responses by phosphorylating the TRAPPII complex. Shaggy-like kinases such as BIN2 integrate a vast number of signaling pathways and, together with receptor complexes at the cell surface, comprise a surveillance system fine-tuned to both biotic and abiotic cues (see text for further detail). BIN2 resides in the plasma membrane (PM) and in the cytosol and TRAPPII resides at the cytosol and in the TGN (Vert and Chory, 2006; Qi et al., 2011; Naramoto et al., 2014; Rybak et al., 2014; Ravikumar et al., 2018). We propose that, in the cytosol, the BIN2-TRAPPII interaction serves in the relay of information from the PM to the TGN. We posit that signal integration and decision-making occur at the AtSK–TRAPPII interface. A surface view of the AtTRAPPII complex with AtTRS120 GSK3 phosphorylation sites facing the predicted active site chamber is depicted as AlphaFold structures of AtTRS120/TRAPPC9 and CLUB/AtTRS130/TRAPPC10 mapped onto the cryo-EM-generated structures of yeast TRAPPII (Mi et al., 2022; see Fig. 3 for a cross-kingdom structural alignment). Downstream of TRAPPII, Rab GTPase cascades are postulated to be implicated in implementing decisions reached by the AtSK–TRAPPII module. We speculate that the phosphorylation status of AtTRS120 modulates the specificity of the putative TRAPPPII GEF activity, thereby differentially activating distinct Rab GTPase cascades. In the lower panel, we show one example of an adaptive growth decision in 10-day-old seedlings (Col-0 wild type). Bar plots depict hypocotyl (green) versus root (beige-brown) lengths. Light: Light-grown seedling with a short hypocotyl and a long root. Dark: A seedling germinated in the dark with a long hypocotyl and a short root. DarkW: Water deprivation in the dark; the hypocotyl is shorter and the root longer than under dark conditions. The dotted green arrow (dark, darkW) represents the incentive for hypocotyl elongation in search of light and the brown arrow (darkW) the incentive for root growth in search of water. Thus, darkW is a “conflict-of-interest” scenario in which hypocotyl and root growth have competing interests (Kalbfuß et al., 2022). Figure generated with https://BioRender.com.

Flow diagram suggesting how BIN2 might mediate plant adaptive responses by phosphorylating the TRAPPII complex. Shaggy-like kinases such as BIN2 integrate a vast number of signaling pathways and, together with receptor complexes at the cell surface, comprise a surveillance system fine-tuned to both biotic and abiotic cues (see text for further detail). BIN2 resides in the plasma membrane (PM) and in the cytosol and TRAPPII resides at the cytosol and in the TGN (Vert and Chory, 2006; Qi et al., 2011; Naramoto et al., 2014; Rybak et al., 2014; Ravikumar et al., 2018). We propose that, in the cytosol, the BIN2-TRAPPII interaction serves in the relay of information from the PM to the TGN. We posit that signal integration and decision-making occur at the AtSK–TRAPPII interface. A surface view of the AtTRAPPII complex with AtTRS120 GSK3 phosphorylation sites facing the predicted active site chamber is depicted as AlphaFold structures of AtTRS120/TRAPPC9 and CLUB/AtTRS130/TRAPPC10 mapped onto the cryo-EM-generated structures of yeast TRAPPII (Mi et al., 2022; see Fig. 3 for a cross-kingdom structural alignment). Downstream of TRAPPII, Rab GTPase cascades are postulated to be implicated in implementing decisions reached by the AtSK–TRAPPII module. We speculate that the phosphorylation status of AtTRS120 modulates the specificity of the putative TRAPPPII GEF activity, thereby differentially activating distinct Rab GTPase cascades. In the lower panel, we show one example of an adaptive growth decision in 10-day-old seedlings (Col-0 wild type). Bar plots depict hypocotyl (green) versus root (beige-brown) lengths. Light: Light-grown seedling with a short hypocotyl and a long root. Dark: A seedling germinated in the dark with a long hypocotyl and a short root. DarkW: Water deprivation in the dark; the hypocotyl is shorter and the root longer than under dark conditions. The dotted green arrow (dark, darkW) represents the incentive for hypocotyl elongation in search of light and the brown arrow (darkW) the incentive for root growth in search of water. Thus, darkW is a “conflict-of-interest” scenario in which hypocotyl and root growth have competing interests (Kalbfuß et al., 2022). Figure generated with https://BioRender.com.

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