Arginine decarboxylase GhADC2 mediates alkali stress tolerance in cotton through polyamine-dependent antioxidant regulation

Arginine decarboxylase (ADC) is a key enzyme in the polyamine biosynthesis pathway, catalyzing the conversion of arginine to putrescine (Put), which plays a critical role in plant stress responses. However, the function of ADC genes in cotton under alkali stress remains poorly understood. In this study, we systematically identified 16 ADC genes across 4 Gossypium species and characterized their phylogenetic relationships, gene structures, and promoter cis -elements. Expression profiling revealed that GhADC2 was the most significantly upregulated member in response to Na 2 CO 3 stress, with relatively high expression in leaves. Subcellular localization analysis showed that GhADC2 was predominantly localized in the nucleus and also exhibited plasma membrane-associated or cell-peripheral signals. Virus-induced gene silencing (VIGS) of GhADC2 in cotton led to reduced Put content, increased reactive oxygen species (ROS) accumulation, enhanced cell death, and decreased antioxidant enzyme activities, indicating compromised alkali tolerance. Conversely, heterologous overexpression of GhADC2 in Arabidopsis thaliana enhanced Put levels, reduced ROS accumulation and cell death, and improved plant growth under alkali stress. Furthermore, exogenous application of Put effectively alleviated alkali stress damage in cotton, restored radicle cell morphology and growth, and increased seedling fresh and dry weights. Yeast heterologous expression assays further confirmed that GhADC2 enhances alkali tolerance. Collectively, our findings demonstrate that GhADC2 positively regulates alkali stress tolerance in cotton by modulating Put biosynthesis and ROS scavenging, offering a promising target for breeding alkali-tolerant cotton varieties.