Kiwifruit (Actinidia chinensis 'Hongyang') cytosolic ascorbate peroxidases (AcAPX1 and AcAPX2) enhance salinity tolerance in Arabidopsis thaliana

Ascorbate peroxidase (APX) plays a key role in scavenging reactive oxygen species (ROS) in higher plants. However, there is very little information available on the APXs in kiwifruit (Actinidia), which is an economically and nutritionally important horticultural crop with exceptionally high ascorbic acid (AsA) accumulation. This study aims to identify and characterize two cytosolic APX genes (AcAPX1 and AcAPX2) derived from A. chinensis 'Hongyang'. The constitutive expression pattern was determined for both AcAPX1 and AcAPX2, and showed relatively higher expression abundances of AcAPX1 in leaf and AcAPX2 in root. Transcript levels of AcAPX1 and AcAPX2 were increased in kiwifruit roots treated with NaCl. Subcellular localization assays using GFP-fusion proteins in Arabidopsis protoplasts showed that both AcAPX1 and AcAPX2 are targeted to the cytosol. Recombinant AcAPX1 or AcAPX2 proteins were successfully expressed in the prokaryotic expression system and their individual ascorbate peroxidase activities were determined. Finally, constitutive over-expression of AcAPX1 or AcAPX2 could dramatically increase total AsA, glutathione level and salinity tolerance under NaCl stress in Arabidopsis thaliana. Our findings revealed that cytosolic AcAPX1/2 may play an important protective role in the responses to unfavorable environmental stimuli in kiwifruit.

Automated summary

This study identified and characterized two cytosolic APX genes (AcAPX1 and AcAPX2) in kiwifruit. The expression pattern and response to NaCl treatment were determined for both AcAPX1 and AcAPX2. The subcellular localization assays showed that both AcAPX1 and AcAPX2 are targeted to the cytosol. Over-expression of AcAPX1 or AcAPX2 increased total ascorbic acid levels and salinity tolerance in Arabidopsis thaliana.