Whole Plant Phenotyping and Molecular Identification of Zn Transporters During Zn Deficiency and Excess in Brachypodium distachyon

Zinc (Zn) is an essential micronutrient for plants and around two billion people are depending on legumes and grains as their main Zn source. This transition metal is however toxic for plants at high concentrations in soils and affects biomass and yield. The eudicot model plant Arabidopsis thaliana has already been characterized for Zn homeostasis under various Zn regimes and recently we have investigated the transcriptome, proteome and ionome upon Zn deficiency and re-supply in this species (Arsova, B. et al., 2019, bioRxiv, 600569). Although some important players of Zn uptake and transport, such as ZRT, IRT-like Protein (ZIP) family genes, have been studied in wheat, rice and barley, it is unclear how different or similar are the responses of monocots and dicots to Zn supply at the molecular level. In the current study, we aim at characterizing Zn regulation in the model plant Brachypodium distachyon. For this, 10-day-old Brachypodium plants were treated with high- and low-Zn medium for two and three weeks. We measured root length, shoot weight and leaf area to examine how Zn supply influences Brachypodium morphology. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis was performed to determine Zn and other metal ion distribution in root and shoot under different Zn treatments. Quantitative RT-PCR analysis of 20 genes orthologous to Arabidopsis Zn homeostasis genes revealed their expression pattern in response to Zn depletion and surplus. We observed the most commonality between Brachypodium and Arabidopsis, as well as the highest correlation between Zn content and gene regulation, for ZIP genes. In general, our results show that comparative molecular study can be useful to reveal the Zn regulatory mechanisms in monocots, which can lead to new Zn biofortification and stress resistance strategies in vital grains