Tonoplast aquaporin aqua1 over-expression modifies poplar (Populus alba L. clone ‘Villafranca’) response to salinity

Salinity is one of the main abiotic stresses for plant survival. In this work, response to salinity was investigated in Populus alba L. clone ‘Villafranca’ transgenic plants over-expressing aqua1, an aquaporin of Populus × canadensis Moench clone ‘I-214’ (GeneBank: GQ918138) and compared to wild-type plants (WT). Two lines with a different level of over-expression were selected. Plants were grown under control conditions (0 mM NaCl) and salinity (100 mM NaCl) for 27 days. At the end of the experiment, transgenic and WT plants were phenotypically indistinguishable. Shoot elongation and total leaf area were reduced equally in all treated plants, even if the relative reduction was lower in transgenic Line 16. The other morphological and physiological parameters measured did not evidence a response correlated to aqua1 over-expression. Interestingly, we observed a decrease in Na concentration in the treated roots of Line 16 compared to WT. Higher polyphenols content in roots and leaves of transgenic Line 16 under control condition was observed. suggesting that aqua1 over-expression has contributed to improve ion regulation and oxidative stress mitigation. These findings revealed that the aqua1 over-expression helps maintain osmotic balance and efficient water transport, contributing to the stability of polyphenol profiles under salinity stress, thereby enhancing tolerance of transgenic lines. Also, our results suggest aqua1 involvement in cell and plant growth and a possible buffering effect of aqua1 over-expression by transcriptional and post-translational modifications that must be further investigated.