AUTHOR=Shao Yuhang, Cheng Yukun, Pang Hongguang, Chang Mingqin, He Fang, Wang Minmin, Davis Destiny J., Zhang Shuxiao, Betz Oliver, Fleck Chuck, Dai Tingbo, Madahhosseini Shahab, Wilkop Thomas, Jernstedt Judy, Drakakaki Georgia TITLE=Investigation of Salt Tolerance Mechanisms Across a Root Developmental Gradient in Almond Rootstocks JOURNAL=Frontiers in Plant Science VOLUME=11 YEAR=2021 URL=https://www.frontiersin.org/articles/10.3389/fpls.2020.595055 DOI=10.3389/fpls.2020.595055 ISSN=1664-462X ABSTRACT=The intensive use of groundwater in agriculture under the current climate conditions leads to acceleration of soil salinization. Given that almond is a salt-sensitive crop, selection of salt-tolerant rootstocks can help maintain productivity under salinity stress. Selection for tolerant rootstocks at an early growth stage can reduce the investment of time and resources. However, salinity-sensitive markers and salinity tolerance mechanisms of almond species to assist this selection process are largely unknown. We established a microscopy-based approach to investigate mechanisms of stress tolerance in and identified cellular, root anatomical, and molecular traits associated with rootstocks exhibiting salt tolerance. We characterized three almond rootstocks: Empyrean-1 (E1), Controller-5 (C5), and Krymsk-86 (K86). Based on cellular and molecular evidence, our results show that E1 has a higher capacity for salt exclusion by a combination of upregulating ion transporter expression and enhanced deposition of suberin and lignin in the root apoplastic barriers, exodermis, and endodermis, in response to salt stress. Expression analyses revealed differential regulation of cation transporters, stress signaling, and biopolymer synthesis genes in the different rootstocks. This foundational study reveals the mechanisms of salinity tolerance in almond rootstocks from cellular and structural perspectives across a root developmental gradient and provides insights for future screens targeting stress response.