Abstract <p>Phosphorus is essential for plant growth, yet its availability in soils is often limited, necessitating phosphorus fertilizers derived from non-renewable resources. This study reports the first successful heterologous expression of the alkaline phosphatase gene (<i>CaAP</i>) from the marine bacterium <i>Cobetia amphilecti</i> in transgenic <i>Nicotiana tabacum</i>. Transgenic lines exhibited enhanced resilience to salt and osmotic stress, as demonstrated by up to 30% higher germination rates, fivefold longer root lengths, and improved membrane stability compared to wild-type (WT) plants. These benefits were linked to increased antioxidant enzyme activity, reduced reactive oxygen species (ROS) levels, lower malondialdehyde (MDA) content, decreased electrolyte leakage, and better maintenance of relative water content. Biochemical analyses revealed significant 1.5- to twofold increases in total phenolic and flavonoid content, along with a marked rise in proline accumulation, suggesting broader metabolic reprogramming. Gene expression profiling confirmed upregulation of key stress-related genes (e.g., <i>SOD</i>, <i>CAT</i>, <i>PHT1</i>, <i>NHX</i>, <i>CHS</i>, <i>P5CS</i>) and downregulation of <i>CDPK</i>, indicating <i>CaAP’s</i> role in transcriptional regulation. However, transgenic plants exhibited reduced performance under calcium-deficient conditions, likely due to the enzyme's calcium dependence, highlighting a trade-off in low-Ca²⁺ environments. These findings underscore the biotechnological potential of marine bacterial phosphatases for engineering stress-resilient crops while identifying critical limitations linked to nutrient context. Further field trials are required to assess the viability of this approach under real-world agricultural conditions.</p> Graphical abstract <p></p>