Figure 11.

Model for the integration of auxin signaling and the PHR1 regulon in the Arabidopsis Pi-starvation response. Under both high- and low-Pi conditions, ARF7 and ARF19 regulate PHR1 in roots. When plants suffer Pi deficiency, PHR1 protein is activated by an unknown mechanism, then its downstream PSI genes are up-regulated. In roots of the arf7 arf19 mutant, PHR1 is inactivated, causing the suppression of molecular responses to Pi starvation. In shoots of the arf7 arf19 mutant, PHR1 expression is intact, and the severe deficiency of Pi results in increased biosynthesis of anthocyanin. In roots of the phr1 mutant, the lateral root initiation dependent on PHR1 is interrupted, resulting in decreased proliferation of lateral roots. In shoots of the phr1 mutant, anthocyanin accumulation dependent on PHR1 is impaired. WT, Wild type.