Overexpression of NtEXPA11 modulates plant growth and development and enhances stress tolerance in tobacco

Apart from providing the much-needed strength, plant cell walls define the shape, size and function of cells. As such, there is a constant change in the cell wall dynamics. These are facilitated by various enzymes and proteins. Expansins are a typical example of those cell wall proteins that are involved in cell wall modifications underlying many plant developmental and physiological processes. In this work, we investigated the role of NtEXPA11 gene in tobacco by generating transgenic plants ectopically expressing NtEXPA11 under the control of CaMV35S promoter. Gene expression analysis revealed that although this gene was present in all the studied tissues in WT plants, its transcript levels were highest in the stems, flowers and leaves and lowest in the roots. Following its overexpressing in tobacco, the NtEXPA11-OX plants exhibited an enhanced growth phenotype. Compared to WT plants, these plants demonstrated an increased growth rate which was characterized by a vigorous root system as well as an accelerated growth rate during their early developmental stages. NtEXPA11-OX plants also developed significantly bigger leaves and internode lengths. They exhibited a 57% increase (NtEXPA11-2) and 98% increase (NtEXPA11-19) in leaf area when grown on MS media. Most interestingly, NtEXPA11-OX plants had significantly bigger pith and parenchyma cells compared to their WT counterparts. Furthermore, we noted that NtEXPA11 plays an important role in plant adaptation to stresses as indicated by the improved tolerance to drought and salt stress of the NtEXPA11-OX plants compared to the WT plants.