Review. Out of shape during stress: a key role for auxin

The plant hormone auxin is a major player in determining root growth and architecture, but we are just starting to understand how auxin distribution is altered by abiotic stresses. Kover et al. discuss how the “upside-down fountain” of auxin in the root is affected by abiotic stress conditions. Auxin transporters not only contribute to the auxin gradient along the root, but also control auxin distribution within the cell, for example by sequestering the auxin in the vacuole or ER and so restricting its accessibility for nuclear signaling. Also, the decrease of the cytoplasmic and apoplastic pH restricts auxin mobility under saline conditions. Although the majority of auxin is believed to be produced in the shoot, genes involved in auxin synthesis are locally upregulated in the root under stress, contributing to the auxin pool and sustaining the growth of the main and lateral roots. The authors argue for the integration of auxin metabolism and local regulation of auxin biosynthesis into mathematical models to better understand how auxin modulates root development under stress conditions. (Summary by Magdalena Julkowska) Trends Plant Sci. 10.1016/j.tplants.2018.05.011