Potentiation of Catalase-Mediated Plant Thermotolerance by N-Terminal Attachment of Solubilizing/Thermostabilizing Fusion Partners

Catalase (CAT) plays a crucial role in plant responses to environmental stresses and maintaining redox homeostasis. However, its putative heat lability might compromise its activity and function, thus restricting plant thermotolerance. Herein, we verified Arabidopsis CAT3 was of poor thermostability that was then engineered by fusion expression in <i>Escherichia coli</i>. We found that our selected fusion partners, three hyperacidic mini-peptides and the short rubredoxin from hyperthermophile <i>Pyrococcus furiosus</i>, were commonly effectual to enhance the solubility and thermostability of CAT3 and enlarge its improvement on heat tolerance in <i>E. coli</i> and yeast. Most importantly, this finding was also achievable in plants. Fusion expression could magnify CAT3-mediated thermotolerance in tobacco. Under heat stress, transgenic lines expressing CAT3 fusions generally outperformed native CAT3 which in turn surpassed wild-type tobacco, in terms of seed germination, seedling survival, plant recovery growth, protection of chlorophyll and membrane lipids, elimination of H₂O₂, as well as mitigation of cell damage in leaves and roots. Moreover, we revealed that the introduced CAT3 or its fusions seemed solely responsible for the enhanced thermotolerance in tobacco. Prospectively, this fusion expression strategy would be applicable to other crucial plant proteins of intrinsic heat instability and thus provide an alternative biotechnological route for ameliorating plant heat tolerance.