The Role of Root-Specific Expression of ZIP Genes in the Control of Zn and Cd Translocation to Shoots

The research contributes to understanding in roots mechanisms controlling efficiency of Zn/Cd translocation to shoots, which depends on combinations of Zn/Cd concentrations in the medium. Previous study showed that this phenomenon was accompanied by differential expression of NtZIP1 and NtZIP4 (ZRT-IRT –like Proteins) in roots [1]. Current research dissects their importance to these processes in more detail. In this study, the role of the apical and basal segments was taken into account.

The NtZIP1 and NtZIP4 were cloned. Transient expression of the fusion constructs 35S::NtZIP1::GFP and 35S::NtZIP4::GFP in tobacco leaves demonstrated their localization to the plasmamembrane. Expression of both genes in wild-type yeasts and zrt1zrt2 mutant showed that Zn and Cd are substrates for both proteins. The real-time-qPCR and expression of NtZIP1p::GUS and NtZIP4p::GUS in tobacco showed that expression of NtZIP1 was specifically detected in the apical part of the roots, and not in the basal one. To compare, NtZIP4 was expressed equally in both root segments. Moreover, it was shown that both genes are expressed in the central cylinder and in the pericycle, but not in the epidermis. Thus they do not contribute to the uptake of Zn and Cd directly from the medium. Moreover, expression of both genes in roots was regulated in examined root segments in a tissue-specific manner which also depends on the combinations of medium Zn/Cd concentrations. Accumulation of Zn and Cd in apical and basal root parts differ depending on the Zn/Cd medium content. Moreover, silencing of NtZIP1 and NtZIP4 led to severe Zn deficiency.

In conclusion, both NtZIP1 and NtZIP4 are key elements involved in the regulation of Zn/Cd dependent translocation of metals to shoots.

[1] Barabasz et al, JExpBot. 2016, 67,6201-6214

Acknowledgement: The research was carried out within the project 2014/15/B/NZ9/02303, financially supported by the NCN, Poland.