Peroxisomal PEX7 Receptor Affects Cadmium-Induced ROS and Auxin Homeostasis in Arabidopsis Root System

Diego Piacentini,Lorenzo Massimi,Adriano Sofo,Giuseppina Falasca,Ilaria Bertoldi,Federica Della Rovere,Maria Maddalena Altamura

doi:10.3390/antiox10091494

Diego Piacentini, Lorenzo Massimi + Show 5 more

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https://doi.org/10.3390/antiox10091494

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Abstract

Peroxisomes are important in plant physiological functions and stress responses. Through the production of reactive oxygen and nitrogen species (ROS and RNS), and antioxidant defense enzymes, peroxisomes control cellular redox homeostasis. Peroxin (PEX) proteins, such as PEX7 and PEX5, recognize peroxisome targeting signals (PTS1/PTS2) important for transporting proteins from cytosol to peroxisomal matrix. pex7-1 mutant displays reduced PTS2 protein import and altered peroxisomal metabolism. In this research we analyzed the role of PEX7 in the Arabidopsis thaliana root system exposed to 30 or 60 μM CdSO4. Cd uptake and translocation, indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) levels, and reactive oxygen species (ROS) and reactive nitrogen species (RNS) levels and catalase activity were analyzed in pex7-1 mutant primary and lateral roots in comparison with the wild type (wt). The peroxisomal defect due to PEX7 mutation did not reduce Cd-uptake but reduced its translocation to the shoot and the root cell peroxisomal signal detected by 8-(4-Nitrophenyl) Bodipy (N-BODIPY) probe. The trend of nitric oxide (NO) and peroxynitrite in pex7-1 roots, exposed/not exposed to Cd, was as in wt, with the higher Cd-concentration inducing higher levels of these RNS. By contrast, PEX7 mutation caused changes in Cd-induced hydrogen peroxide (H2O2) and superoxide anion (O2●−) levels in the roots, delaying ROS-scavenging. Results show that PEX7 is involved in counteracting Cd toxicity in Arabidopsis root system by controlling ROS metabolism and affecting auxin levels. These results add further information to the important role of peroxisomes in plant responses to Cd.

Highlights

Peroxisomes play important roles in a wide range of plant physiological functions, including primary and secondary metabolism, development, and stress responses
Both primary root (PR) elongation and lateral roots (LRs) formation and elongation are negatively affected by Cd, and the indole-3-butyric acid (IBA)-to-indole-3-acetic acid (IAA) conversion is reduced in the presence of pex7-1 mutation, with this altering the auxin balance in the mutant roots
Results demonstrate that well-functioning peroxisomes are indispensable to the Arabidopsis thaliana root system for reacting to Cd, and that a correct import of PTS2-proteins by PEX7 into the peroxisomal matrix is essential for reactive oxygen species (ROS) scavenging action, and for controlling auxin homeostasis

Summary

Introduction

Peroxisomes play important roles in a wide range of plant physiological functions, including primary and secondary metabolism, development, and stress responses. In the latter responses, they work through the production of reactive oxygen species (ROS), reactive nitrogen species (RNS), and antioxidant defense enzymes [1,2]. They work through the production of reactive oxygen species (ROS), reactive nitrogen species (RNS), and antioxidant defense enzymes [1,2] These organelles have an oxidative metabolism characterized by high levels of hydrogen peroxide (H2 O2 ), as a ROS, and by the presence of catalase (CAT), as an H2 O2 -scavenging enzyme [3]. The β-oxidation of the auxin precursor indole-3-butyric acid (IBA) into the active

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