Specific redox and iron homeostasis responses in the root tip of Arabidopsis upon zinc excess

Abstract

O_LIZinc (Zn) excess negatively impacts primary root growth in Arabidopsis. Yet, the effects of Zn excess on specific growth processes in the root tip remain largely unexplored. C_LIO_LITranscriptomics, ionomics and metabolomics were used to examine the specific impact of Zn excess on the root tip (RT) compared to the remaining root (RR). C_LIO_LIZn excess exposure resulted in shortened root apical meristem and elongation zone, with differentiation initiating closer to the tip of the root. Zn accumulated at a lower concentration in the RT than in RR. This pattern was associated with lower expression of Zn homeostasis and Fe deficiency response genes. C_LIO_LIA distinct distribution of Zn and Fe in RT and RR was highlighted by Laser Ablation ICP-MS analysis. C_LIO_LISpecialized Trp-derived metabolism genes, typically associated with redox and biotic stress responses, were specifically up-regulated in the RT upon Zn excess, among those Phytoalexin Deficient 3 (PAD3) encoding the last enzyme of camalexin synthesis. In roots of wild-type seedlings, camalexin concentration increased by 6-fold upon Zn excess and a pad3 mutant displayed increased Zn sensitivity and an altered ionome. C_LIO_LIOur results indicate that distinct redox and iron homeostasis mechanisms are key elements of the response to Zn excess in the RT. C_LI