Environmental nitrate signals through abscisic acid in the root tip.

ABSTRACT

Roots respond to changes in environmental nitrate with a localized stimulation of ABA levels in the root tip. This rise in ABA levels is due to the action of ER-localized ß-GLUCOSIDASE 1, which releases bioactive ABA from the inactive ABA-glucose ester. The slow rise in root tip ABA levels stimulates expression of nitrate metabolic enzymes and simultaneously activates a negative feedback loop involving the protein phosphatase, ABI2, which reduces nitrate influx via the AtNPF6.3 transceptor. The rise in root-tip localized ABA also negatively regulates expression of the SCARECROW transcription factor, thus providing a sensitive mechanism for modulating root growth in response to environmental changes.