Constitutively and highly expressed Oryza sativa polyamine oxidases localize in peroxisomes and catalyze polyamine back conversion

摘要

Polyamine oxidases (PAOs) are FAD-depen-dent enzymes involved in polyamine (PA) catabolism. Recent studies have revealed that plant PAOs are not only active in the terminal catabolism of PAs as demonstrated for maize apoplastic PAO but also in a polyamine back-conversion pathway as shown for most Arabidopsis PAOs. We have characterized Oryza sativa PAOs at molecular and biochemical levels. The rice genome contains 7 PAO isoforms that are termed OsPAOl to OsPAO7. Of the seven PAOs, OsPA03, OsPA04, and OsPAOS transcripts were most abundant in 2-week-old seedlings and mature plants, while OsPAOl, OsPAOl, OsPA06, and OsPA07 were expressed at very low levels with different tissue specificities. The more abundantly expressed PAOs-OsPA03, OsPAO4, and OsPAO5-were cloned, and their geneproducts were produced in Escherichia coli. The enzymatic activities of the purified OsPA03 to OsPAOS proteins were examined. OsPAOS favored spermidine (Spd) as substrate followed by thermospermine (T-Spm) and spermine (Spm) and showed a full PA back-conversion activity. OsPA04 substrate specificity was similar to that of OsPAOS preferring Spm and T-Spm but not Spd. Those enzymes also converted Spm and T-Spm to Spd, again indicative of PA back-conversion activities. Lastly, we show that OsPA03, OsPA04, and OsPAOS are localized in peroxisomes. Together, these data revealed that constitutively and highly expressed O. sativa PAOs are localized in peroxisomes and catalyze PA back-conversion processes.