Evolution and Expression Analysis of PAO Gene Family in Cotton: Focusing on Fiber Development and Stress Response

Polyamines, a class of low-molecular-weight nitrogen-containing bases with high biological activity, are ubiquitous in organisms and play protective roles in plants under stress. Polyamine oxidase (PAO), a typical flavoprotein characterized as a glycoprotein, is a key enzyme in polyamine catabolism that directly mediates polyamine breakdown and maintains intracellular polyamine homeostasis. However, the specific functions of PAOs in cotton fiber development remain largely unclear. In this study, we identified 23 GhPAO genes from the upland cotton (Gossypium hirsutum L.) genome via comprehensive bioinformatics approaches. We systematically analyzed their physicochemical properties, phylogenetic relationships, gene structures, chromosomal locations, conserved motifs, cis-acting elements, and expression patterns. Quantitative real-time PCR (qPCR) analysis confirmed that GhPAO10 and GhPAO21 exhibited the most pronounced transcript accumulation during both fiber development and stress response processes. Further yeast one-hybrid (Y1H) and dual-luciferase reporter assays indicated that the GhPAO21 promoter was directly regulated by the transcription factor GhTGA1. Our findings provide a foundation for elucidating the functional roles of the PAO gene family in upland cotton and underscore potential candidate genes associated with fiber development and stress responses.