Provide a mechanistic link between auxin and plasma membrane H(+)-ATPases (PM H(+)-ATPases, e.g. AHA1 and AHA2), and triggers PM H(+)-ATPases activity by promoting phosphorylation of their C-terminal autoinhibitory domain as a result of PP2C-D subfamily of type 2C phosphatases inhibition, thus leading to the acidification of the apoplast and the facilitation of solutes and water uptake to drive cell expansion (By similarity). Triggers plant growth probably by promoting cell elongation (PubMed:28586421, PubMed:29258424). Regulates branch angles and bending (PubMed:28586421, PubMed:29258424). Confined to the veins and petioles of rosette leaves and cauline leaves, and specifically expressed at the abaxial side of inflorescence branche; relocates to both the adaxial (Ad) and abaxial (Ab) sides of the branch in reduced red:far-red (R:FR) light, during shade (PubMed:28586421, PubMed:29258424). Also present in flowers (PubMed:28586421, PubMed:29258424). Appears at later stages of developing flowers, in the vasculature of the style, and in the apical parts of the stamen filaments and petals. Induced by auxin (e.g. 2,4D) (PubMed:16024589, PubMed:28586421, PubMed:29258424). Up-regulated by brassinosteroids (e.g. brassinolide) (PubMed:29258424). Highly induced by a synergistic combination of auxin (e.g. IAA) and brassinolide. Accumulates in response to reduced red:far-red (R:FR) light, during shade; this light response can be attenuated by AGL8/FUL in the stem. Repressed by AGL8/FUL in stems and inflorescence branches (PubMed:28586421). Accumulates in reduced red/far-red light ration (R:FR) conditions mimicking shaded conditions (PubMed:29258424). Belongs to the ARG7 family.