The distal axis (QC, columella, and LRC) regulates both cell division and differentiation gradients by long-distance influence (e.g., RGFs and miR396). The proximal axis (radial cell files) has top-down influence, setting the position of the QC, the upper-most cell of the distal axis, through SCR/SHR and ROW1. These factors influence distal axis division and differentiation through QC factors and potentially other long distance mechanisms to affect columella identity (not shown).