Subfunctionalization of Parental Polyamine Oxidase (PAO) Genes in the Allopolyploid Tobacco (L.).

Polyamines play an important role in developmental and environmental stress responses in plants. Polyamine oxidases (PAOs) are flavin-adenine-dinucleotide-dependent enzymes associated with polyamine catabolism. In this study, 14 genes were identified in the tobacco genome that code for PAO proteins being named based on their sequence homology with Arabidopsis PAOs (AtPAO1-5): NtPAO1A-B; NtPAO2A-C, NtPAO4A-D, and NtPAO5A-E. Sequence analysis confirmed that the gene family of the allopolyploid hybrid is not an exact combination of the genes of the maternal and paternal ones. The loss of the homeolog of and the gain of an extra copy, likely of origin, was revealed. The latter adds to the few pieces of evidence suggesting that the paternal parent of was an introgressed hybrid of and . Gene expression analysis indicated that all 14 genes kept their expression following the formation of the hybrid species. The homeologous gene pairs showed similar or opposite regulation depending on the investigated organ, applied stress, or hormone treatment. The data indicate that the expression pattern of the homeologous genes is diversifying in a process of subfunctionalization.