Cotton metallothionein GhMT3a, a reactive oxygen species scavenger, increased tolerance against abiotic stress in transgenic tobacco and yeast

A cDNA clone encoding a 64-amino acid type 3 metallothioneinprotein, designated GhMT3a, was isolated from cotton (Gossypiumhirsutum) by cDNA library screening. Northern blot analysisindicated that mRNA accumulation of GhMT3a was up-regulatednot only by high salinity, drought, and low temperature stresses,but also by heavy metal ions, abscisic acid (ABA), ethylene,and reactive oxygen species (ROS) in cotton seedlings. Transgenictobacco (Nicotiana tabacum) plants overexpressing GhMT3a showedincreased tolerance against abiotic stresses compared with wild-typeplants. Interestingly, the induced expression of GhMT3a by salt,drought, and low-temperature stresses could be inhibited inthe presence of antioxidants. H₂O₂ levels in transgenic tobaccoplants were only half of that in wild-type (WT) plants undersuch stress conditions. According to in vitro assay, recombinantGhMT3a protein showed an ability to bind metal ions and scavengeROS. Transgenic yeast overexpressing GhMT3a also showed highertolerance against ROS stresses. Taken together, these resultsindicated that GhMT3a could function as an effective ROS scavengerand its expression could be regulated by abiotic stresses throughROS signalling. Key words: Abiotic stress, antioxidant, GhMT3a, ROS, transgenic tobacco, yeast