Divide Et Impera--cellular auxin compartmentalization.

The phytohormone auxin is an essential regulator for plant growth and development. Decades of intensive research revealed the mutual importance of auxin metabolism and intercellular cell-to-cell transport for the regulation of spatiotemporal auxin distribution. Just recently, intracellular putative auxin carriers, such as the PIN-FORMED (PIN)5/PIN8 and the PIN-LIKES (PILS)2/PILS5 were discovered at the endoplasmic reticulum (ER) and seem to limit nuclear auxin signaling via an auxin sequestration mechanism. Moreover, these auxin carriers at the ER might provide a link between auxin compartmentalization and auxin conjugation-based metabolism. Here we review the recent findings on auxin compartmentalization at the ER and discuss its potential contribution to cellular auxin homeostasis and its importance for plant development.