Insights on Zn deficiency and Zn excess effects on the Root Apical Meristem in Arabidopsis

Zinc, an essential cofactor to many enzymes, is an important micronutrient in plants. Crop culture on Zn deficient soils, which are widespread worldwide, is limiting productivity and quality and is considered as a concern for human nutrition. In contrast, with industrialisation, soils were contaminated in large areas with toxic metal concentrations including Zn. To address both issues of Zn deficiency and Zn excess, it is required to better understand the responses to variation in Zn supply in plants, which will enable the design of efficient biofortification or phytoremediation strategies, respectively. Root growth is regulated at the root apex, where mitosis, as well as cell elongation and differentiation occur. Zn deficiency and excess are known to have an effect on root growth, for instance by affecting auxin production and Reactive Oxygen species (ROS) levels in the Root Apical Meristem (RAM). However, a detailed investigation on the delicately balanced regulation of the root meristematic activity by Zn is still missing. In this study, root responses to Zn deficiency and Zn excess were examined in Arabidopsis. We re-assessed RAM activity upon both Zn deficiency and Zn excess and observed distinct effects of both treatments on cell elongation and differentiation, as well as on the cell cycle itself. To better pinpoint which specific processes are affected by altered Zn nutrition, RNA-Seq datasets were generated for root tips versus differentiated roots comparing normal Zn supply to Zn excess or Zn deficiency. We observed root tip specific responses and identified potential candidate genes (e.g. transporters, hormonal response, cell-wall) for involved in these responses Zn supply imbalance. Furthermore, linking the RNA-Seq datasets with Zn localization in root tissues by Laser Ablation-ICP-MS experiments and publicly available single-cell transcriptional maps provided a detailed assessment of the RAM response to Zn supply.