Tissue-Autonomous Phenylpropanoid Production is Essential for Establishment of Root Barriers

Abstract

Plants deposit polymeric barriers in their root cell walls to protect inner tissues and facilitate selective uptake of solutes. Insights into how individual root tissues contribute to formation are important for elucidation of ultrastructure, function and development of barriers. Although the machinery responsible for production of the constituents is well-characterized, our models of the underlying pathways lack spatiotemporal resolution – especially in roots -, thus, the source of monomeric barrier components is not clear. This is mainly due to restricted ability to manipulate the wide-functioning phenylpropanoid synthesis, as mutants in this pathway often display lethal or pleiotropic phenotypes. Here, we overcome this challenge by exploiting highly controlled in vivo repression. We provide strong evidence that autonomous production of phenylpropanoids is essential for establishment of the endodermal Casparian strip and adherence of the suberin matrix to the cell wall of endodermis and cork. Our work highlights that, in roots, the phenylpropanoid pathway is under tight spatiotemporal control and serve distinct roles in barrier formation across tissues and developmental zones. This becomes evident in the late endodermis, where repression of phenylpropanoid production leads to active removal of suberin in pre-suberized cells, indicating that endodermal suberin depositions might embody a steady-state between continuous synthesis and degradation.