Generating salt-tolerant Nicotiana tabacum and identification of stress-responsive miRNAs in transgenics

Identification of vacuolar Na+/H+ antiporters facilitates the basis of salt stress tolerance mechanisms. Na+ accumulation into the vacuole is crucial for the avoidance of cytoplasmic Na+ toxicity. In this study, we show that the introduction of AtNHX1 into tobacco generated more tolerant plants when compared to wild-type plants. Transgenic tobacco plants exhibited higher germination rates in the presence of increasing salt concentrations compared to wild-type plants. In addition, proline levels were higher under salt stress conditions in both the shoots and the roots of transgenics compared to wild-type plants. Increase in malondialdehyde production during lipid peroxidation by salinity was lower in transgenic plants compared to the controls. Being important and newly discovered determiners of plant stress responses, microRNAs (miRNAs) are noncoding small RNAs and essential indicators of plant stress response mechanisms. For further identification of stress responses, the expression levels of growth and abiotic stress-related miRNAs (miR319a, miR319b, miR159b, miR398a, and miR398b) were quantified. miR319a, miR319b, and miR159b expression levels were higher in wildtype plants, and miR319a and miR159b expression was restored in transgenic plants. There was a slight decrease in the expression levels of miR398a and miR398b of wild-type plants. However, the recovery of the miR398a and miR398b expressions was especially significant in transgenic plants. Furthermore, an investigation of miRNAs in transgenic plants can help to understand the stress tolerance mechanisms of the plants