Figure 9. Schematic model of the role of PIN2 and phosphorylation in root nitrate responses.

Nitrate treatments increase cytosolic calcium levels which interact with calcium‐binding proteins such as kinases in the nitrate signaling pathway. Kinases phosphorylate protein targets such as transcription factors that can mediate changes in gene expression in response to nitrate treatments. Nitrate can also cause dephosphorylation of specific proteins. We showed nitrate treatments promote PIN2 dephosphorylation at S439 which impact membrane localization and polarity of the PIN2 protein. This post‐translational regulatory mechanism is important for modulation of primary root growth and lateral root density in response to nitrate treatments. Arrows and bar‐headed solid lines represent activation or inhibition in response to nitrate, respectively. Dashed arrows indicate proposed connections. A working model (depicted in synopsis image) was constructed with the BioRender.com software.