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. 2021 Aug 30;187(4):2043–2055. doi: 10.1093/plphys/kiab343

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© The Author(s) 2021. Published by Oxford University Press on behalf of American Society of Plant Biologists.

This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs licence (https://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reproduction and distribution of the work, in any medium, provided the original work is not altered or transformed in any way, and that the work is properly cited. For commercial re-use, please contact journals.permissions@oup.com

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A model for PP-InsP sensing by SPX domain proteins in plants. Under Pi-replete conditions (A), high cellular Pi and ATP levels drive InsP₈ synthesis, which promotes the PHR–SPX interaction and thus suppresses the activation of PSR genes. Under Pi-depleted conditions (B), the decrease of cellular Pi and ATP results in a decline of InsP₈ level. Accordingly, PHR1 is released to activate PSR genes. Expression of nitrate-responsive genes (NiR) and senescence-associated genes (SAG) is also activated by NLP3 and ORE1, respectively. It is likely that changes in the InsP₈ level also regulates the activity of other SPX-domain proteins, including NLA, PHO1, and PHT5 involved in Pi acquisition, translocation, and storage, respectively. MRP5 is a vacuolar InsP₆ transporter. Thickness of arrows indicates the strength of activities. C, A summary of proteins interacting with SPX domain-containing proteins and their mediated physiological responses (see text for details).

Inline graphic — A model for PP-InsP sensing by SPX domain proteins in plants. Under Pi-replete conditions (A), high cellular Pi and ATP levels drive InsP₈ synthesis, which promotes the PHR–SPX interaction and thus suppresses the activation of PSR genes. Under Pi-depleted conditions (B), the decrease of cellular Pi and ATP results in a decline of InsP₈ level. Accordingly, PHR1 is released to activate PSR genes. Expression of nitrate-responsive genes (NiR) and senescence-associated genes (SAG) is also activated by NLP3 and ORE1, respectively. It is likely that changes in the InsP₈ level also regulates the activity of other SPX-domain proteins, including NLA, PHO1, and PHT5 involved in Pi acquisition, translocation, and storage, respectively. MRP5 is a vacuolar InsP₆ transporter. Thickness of arrows indicates the strength of activities. C, A summary of proteins interacting with SPX domain-containing proteins and their mediated physiological responses (see text for details).