Outer apoplastic barriers in roots: prospects for abiotic stress tolerance

Floods and droughts are becoming more frequent as a result of climate change and it is imperative to find ways to enhance the resilience of staple crops to abiotic stresses. This is crucial to sustain food production during unfavourable conditions. Here, we analyse the current knowledge about suberised and lignified outer apoplastic barriers, focusing on the functional roles of the barrier to radial O2 loss formed as a response to soil flooding and we discuss whether this trait also provides resilience to multiple abiotic stresses. The barrier is composed of suberin and lignin depositions in the exodermal and/or sclerenchyma cell walls. In addition to the important role during soil flooding, the barrier can also restrict radial water loss, prevent phytotoxin intrusion, salt intrusion and the main components of the barrier can impede invasion of pathogens in the root. However, more research is needed to fully unravel the induction pathway of the outer apoplastic barriers and to address potential trade-offs such as reduced nutrient or water uptake. Nevertheless, we suggest that the outer apoplastic barriers might act as a jack of all trades providing tolerance to multiple abiotic and/or biotic stressors. The outer apoplastic barriers in roots are beneficial for plants growing in flooded soils and could also increase salinity and drought tolerance. We discuss how the outer aposplastic barriers support plant resilience during flooding and new discoveries in relation to conditions of water deficit. We also highlight the mechanisms by which the barrier helps during flooding or drought, the current understanding of its genetic regulation, and the potential side-effects of this trait in various circumstances and in different scenarios.This article belongs to the collection Flooding Stress and Hypoxic Responses in Plants.