Ornithine decarboxylase regulates putrescine-related metabolism and pollen development in Atropa belladonna

Polyamines, including putrescine, spermidine, and spermine, play critical roles in cell physiology by different forms. As a rate-limiting enzyme that converts ornithine to putrescine, ornithine decarboxylase (ODC, EC 1.1.1.37) has been studied in detail in animals and microorganisms, but its specific functions are poorly understood in plants. In this study, the metabolic and developmental roles of the ODC gene were studied through RNAi-mediated suppression of the ODC gene (AbODC) in A. belladonna. Suppression of AbODC reduced the production of precursors of medicinal tropane alkaloids, including putrescine and N-methylputrescine, as well as hyoscyamine and scopolamine. In AbODC-RNAi roots, the production of putrescine and spermidine in free form was reduced, but in the AbODC-RNAi leaves, the content of free polyamines was not altered. In the roots/leaves of AbODC-RNAi plants, the production of conjugated and bound polyamines was reduced. In addition, suppression of the ODC gene resulted in reduction of polyamines and pollen sterility in AbODC-RNAi flowers. In floral organs, GUS-staining results indicated that AbODC was domainantly expressed in pollen. In summary, ornithine decarboxylase not only plays a key role in regulating the biosynthesis of diverse forms of polyamines and medicinal tropane alkaloids, but also participates in pollen development.