Ectopic Expression of Aeluropus littoralis Plasma Membrane Protein Gene AlTMP1 Confers Abiotic Stress Tolerance in Transgenic Tobacco by Improving Water Status and Cation Homeostasis

Abstract

We report here the isolation and functional analysis of <i>AlTMP1</i> gene encoding a member of the PMP3 protein family. In <i>Aeluropus littoralis</i>, <i>AlTMP1</i> is highly induced by abscisic acid (ABA), cold, salt, and osmotic stresses. Transgenic tobacco expressing <i>AlTMP1</i> exhibited enhanced tolerance to salt, osmotic, H₂O₂, heat and freezing stresses at the seedling stage. Under greenhouse conditions, the transgenic plants showed a higher level of tolerance to drought than to salinity. Noteworthy, <i>AlTMP1</i> plants yielded two- and five-fold more seeds than non-transgenic plants (NT) under salt and drought stresses, respectively. The leaves of <i>AlTMP1</i> plants accumulated lower Na⁺ but higher K⁺ and Ca²⁺ than those of NT plants. Tolerance to osmotic and salt stresses was associated with higher membrane stability, low electrolyte leakage, and improved water status. Finally, accumulation of <i>AlTMP1</i> in tobacco altered the regulation of some stress-related genes in either a positive (<i>NHX1</i>, <i>CAT1</i>, <i>APX1</i>, and <i>DREB1A</i>) or negative (<i>HKT1</i> and <i>KT1</i>) manner that could be related to the observed tolerance. These results suggest that <i>AlTMP1</i> confers stress tolerance in tobacco through maintenance of ion homeostasis, increased membrane integrity, and water status. The observed tolerance may be due to a direct or indirect effect of <i>AlTMP1</i> on the expression of stress-related genes which could stimulate an adaptive potential not present in NT plants.