The promoter of the Arabidopsis PIN6 auxin transporter enabled strong expression in the vasculature of roots, leaves, floral stems and reproductive organs

Cellular auxin homeostasis controls many aspects of plant growth, organogenesis and development. The existence of intracellular auxin transport mediated by endoplasmic reticulum (ER)-localized PIN 5, PIN 6 and PIN 8 proteins is a relatively recent discovery shaping a new era in understanding auxin-mediated growth processes. Here we summarize the importance of PIN 6 in mediating intracellular auxin transport during root formation, leaf vein patterning and nectar production. While, it was previously shown that PIN6 was strongly expressed in rosette leaf cell types important in vein formation, here we demonstrate by use a PIN6 promoter-reporter fusion, that PIN6 is also preferentially expressed in the vasculature of the primary root, cotyledons, cauline leaves, floral stem, sepals and the main transmitting tract of the reproductive silique. The strong, vein- specific reporter gene expression patterns enabled by the PIN6 promoter emphasizes that transcriptional control is likely to be a major regulator of PIN 6 protein levels, during vasculature formation, and supports the need for ER-localized PIN proteins in selecting specialized cells for vascular function in land plants.