Figure 4.

Model depicting how PP-InsPs regulate plant Pi sensing and the Pi starvation response (PSR). (a) PSR gene regulation under deplete (top) and replete Pi conditions (bottom). SPX1 binds to PHR1 under replete Pi, preventing SPX1 from binding to promoters containing P1BS. Under deplete Pi, PHR1 is uninhibited from binding to P1BS promoters. Adapted from [60]. (b) Model depicting a complex formation between SPX1, PHR1, and InsP₈. This model represents interactions between other SPX proteins and PSR regulators, such as PHR1 and its homolog, PHT1, along with others.