Crosstalk between the Glutathione Peroxidase-Like 5 Isoenzyme (AtGPXL5) and Ethylene.

Glutathione peroxidases (GPXs) are important antioxidant enzymes in animals. Plants contain GPX-like (GPXL) enzymes, which-in contrast to GPXs-contain cysteine in their active site instead of selenocysteine. Although several studies proved their importance in development and stress responses, their interaction with ethylene (ET) signalling is not known. Our aim was to investigate the involvement of AtGPXL5 in ET biosynthesis and/or signalling using mutant and cDNA-overexpressing (OX-AtGPXL5) lines. Four-day-old dark-grown seedlings had shorter hypocotyls and primary roots, while OX-AtGPXL5 seedlings exhibited a similar phenotype as wild type under normal conditions. Six-week-old OX-AtGPXL5 plants contained less HO and malondialdehyde, but higher polyamine and similar ascorbate- and glutathione contents and redox potential () than the Col-0. One-day treatment with the ET-precursor 1-aminocyclopropane-1-carboxylic acid (ACC) induced the activity of glutathione- and thioredoxin peroxidases and some other ROS-processing enzymes. In the mutants, the became more oxidised; parallelly, it produced more ethylene after the ACC treatment than other genotypes. Although the enhanced ET evolution measured in the mutant can be the result of the increased ROS level, the altered expression pattern of ET-related genes both in the and OX-AtGPXL5 plants suggests the interplay between AtGPXL5 and ethylene signalling.