Genome-wide identification and expression analysis of the polyamine oxidase gene family in soybean

Polyamine oxidases (PAOs) are flavin adenine dinucleotide-dependent enzymes that are involved in polyamine catabolism and play an essential role in growth and developmental processes as well as the response to abiotic stresses. Although the PAO gene families have been intensively studied in many plants, the soybean (Glycine max (L.) Merr.) PAO gene family has not been systematically identified. Here, we identified six PAO genes in the soybean genome and named them GmPAO1-GmPAO6. The phylogenetic analysis revealed that plant PAO proteins are divided into four classes. GmPAO1 and GmPAO4 belong to class I; GmPAO2, GmPAO5, and GmPAO6 belong to class IV. Similar to most dicotyledonous plants, soybeans do not contain class II. Interestingly, we identified an additional SWIRM-domain PAO gene GmPAO3, which exists between classes III and IV. GmPAO3 had a different gene structure and expression. To determine the individual roles of GmPAOs, we analyzed their expression levels in various tissues and under abiotic stress. Each GmPAO gene can respond in a specific tissue under specific abiotic stress. The data can help to clarify the role of GmPAOs in abiotic stress responses in soybean and provide a breeding basis for enhancing soybean tolerance to abiotic stresses.