Abstract
Polyamines (PAs), including putrescine, spermidine, spermine, and thermospermine, play essential roles in plant growth, development, and responses to stress. However, the structure and function of PA biosynthetic genes in pepper remain poorly characterized. This study aimed to identify PA biosynthesis genes in the pepper genome using bioinformatics approaches and to assess their expression under various stress conditions. A total of 16 PA biosynthesis-related genes were identified, representing members of the arginine decarboxylase (ADC), ornithine decarboxylase (ODC), agmatine iminohydrolase (AIH), N-carbamoylputrescine amidohydrolase (CPA), S-adenosylmethionine decarboxylase (SAMDC), spermidine synthase (SPDS), spermine synthase (SPMS), and ACAULIS5 (ACL5) gene families. These genes encode proteins with an average molecular weight of approximately 40 kDa, primarily localized in the mitochondria and cytoplasm. Promoter analysis revealed multiple cis-acting elements associated with stress and phytohormone responsiveness. Gene expression was induced by various abiotic stresses, including saline-alkaline, drought, heat, cold, and hydrogen peroxide, as well as by phytohormones such as abscisic acid, ethylene, salicylic acid, auxin, and gibberellin. Overall, this study provides a comprehensive analysis of PA biosynthesis genes in pepper and highlights their potential roles in stress adaptation and hormone signalling, offering a foundation for further exploration of PA-mediated stress tolerance mechanisms.