Kandelia candel Thioredoxin f Confers Osmotic Stress Tolerance in Transgenic Tobacco

• Main Authors: Xiaoshu Jing, Jun Yao, Xujun Ma, Yanli Zhang, Yuanling Sun, Min Xiang, Peichen Hou, Niya Li, Rui Zhao, Jinke Li, Xiaoyang Zhou, and Shaoliang Chen
• Format: Article
• Language: English
• Published: MDPI AG 2020-05-01
• Series: International Journal of Molecular Sciences
• Subjects: thioredoxin; Kandelia candel; mannitol; drought; water retaining capacity; soluble sugar
• Online Access: https://www.mdpi.com/1422-0067/21/9/3335

Water deficit caused by osmotic stress and drought limits crop yield and tree growth worldwide. Screening and identifying candidate genes from stress-resistant species are a genetic engineering strategy to increase drought resistance. In this study, an increased concentration of mannitol resulted in elevated expression of thioredoxin f (<i>KcTrxf</i>) in the nonsecretor mangrove species <i>Kandelia candel</i>. By means of amino acid sequence and phylogenetic analysis, the mangrove Trx was classified as an f-type thioredoxin. Subcellular localization showed that KcTrxf<i> </i>localizes to chloroplasts. Enzymatic activity characterization revealed that KcTrxf recombinant protein possesses the disulfide reductase function. <i>KcTrxf</i> overexpression contributes to osmotic and drought tolerance in tobacco in terms of fresh weight, root length, malondialdehyde (MDA) content, and hydrogen peroxide (H₂O₂) production. KcTrxf was shown to reduce the stomatal aperture by enhancing K⁺ efflux in guard cells, which increased the water-retaining capacity in leaves under drought conditions. Notably, the abscisic acid (ABA) sensitivity was increased in <i>KcTrxf</i>-transgenic tobacco, which benefits plants exposed to drought by reducing water loss by promoting stomatal closure. <i>KcTrxf</i>-transgenic plants limited drought-induced H₂O₂ in leaves, which could reduce lipid peroxidation and retain the membrane integrity. Additionally, glutathione (GSH) contributing to reactive oxygen species (ROS) scavenging and transgenic plants are more efficient at regenerating GSH from oxidized glutathione (GSSG) under conditions of drought stress. Notably, <i>KcTrxf</i>-transgenic plants had increased glucose and fructose contents under drought stress conditions, presumably resulting from KcTrxf-promoted starch degradation under water stress. We conclude that KcTrxf contributes to drought tolerance by increasing the water status, by enhancing osmotic adjustment, and by maintaining ROS homeostasis in transgene plants.