Molecular cloning and functional analysis of the thioredoxin gene SikTrxh from Saussurea involucrata

Thioredoxins are oxidoreductases that help to maintain redox homeostasis in plants under abiotic stress. In this study, a new thioredoxin gene, SikTrxh, was cloned from Saussurea involucrata (Kar. & Kir.), a perennial herb that grows in the high alpine mountains of Central Asia. Bioinformatics analysis shows that the full-length cDNA of SikTrxh consisted of 565 bp with a 354-bp open reading frame and encoded a 117 amino acid protein. Using quantitative reverse transcription (RT) PCR, we found that the expression of the SikTrxh gene was induced by salt, cold, and drought stresses, suggesting that this protein played a significant role in plant defense. Subcellular localization confirmed that the protein was localized to the mitochondria. A vector carrying SikTrxh was inserted into tobacco, and successfully modified plants were identified by RT-PCR. Physiological indicators and antioxidant enzyme activities were measured under low temperature, and salt and drought stresses. Our results show that malondialdehyde content and relative electrolyte leakage increased in both wild-type and SikTrxh-overexpressing transgenic plants; however, these increases were significantly higher in the wild-type plants than in the transgenic plants. We also found that photosystem II photoinhibition was lower in the transgenic plants than in the wild-type plants, and that activities of reactive oxygen species-scavenging enzymes were higher in the transgenic plants than in the wild-type plants. We conclude that SikTrxh can reduce toxic effects of reactive oxygen species to protect the plasma membrane, thereby increasing plant resistance to abiotic stresses.