Abstract

In yeast (Saccharomyces cerevisiae) and plant roots (Arabidopsis thaliana) zinc enters the cells via influx transporters of the ZIP family. Since zinc is both essential for cell function and toxic at high concentrations, tight regulation is essential for cell viability. We provide new insight into the underlying mechanisms, starting from a general model based on ordinary differential equations and adapting it to the specific cases of yeast and plant root cells. In yeast, zinc is transported by the transporters ZRT1 and ZRT2, which are both regulated by the zinc-responsive transcription factor ZAP1. Using biological data, parameters were estimated and analyzed, confirming the different affinities of ZRT1 and ZRT2 reported in the literature. Furthermore, our model suggests that the positive feedback in ZAP1 production has a stabilizing function at high influx rates. In plant roots, various ZIP transporters play a role in zinc uptake. Their regulation is largely unknown, but bZIP transcription factors are thought to be involved. We set up three putative models based on: an activator only, an activator with dimerization and an activator-inhibitor pair. These were fitted to measurements and analyzed. Simulations show that the activator-inhibitor model outperforms the other two in providing robust and stable homeostasis at reasonable parameter ranges.

Highlights

  • Zinc is a heavy metal and micronutrient that plays an important role in all living organisms and is essential for the growth of higher green plants [1]

  • It has been reported to protect plant cells from oxidative stress mediated by reactive oxygen species (ROS) [2] and may act as an intracellular second messenger [3]

  • Zinc ions are transported with high affinity by ZRT1 and with low affinity by ZRT2, which both belong to the ZIP family

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Summary

Introduction

Zinc is a heavy metal and micronutrient that plays an important role in all living organisms and is essential for the growth of higher green plants [1]. In plant roots as well as in yeast cells, adaptation of the expression of influx transporters poses the major component of zinc regulation [17,18]. PnT aj Tj f (Ze,Kjt){ PnE bjEj f (Z,Kje){c Z , j~1 j~1 where Z and Ze are the cytosolic and external zinc concentrations, respectively, Ai are activators, Ii inhibitors, Ti and Ei influx and efflux transporters, respectively, Gi and Mi the levels of gene expression and mRNA of Ti, respectively, and pAi and pIi are model dependent production terms.

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