Oryza sativa polyamine oxidase 1 back-converts tetraamines, spermine and thermospermine, to spermidine
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Oryza sativa polyamine oxidase 1 back-converts spermine (or thermospermine) to spermidine. Considering the previous work, major path of polyamine catabolism in rice plant is suggestive to be back-conversion but not terminal catabolism.
Rice (Oryza sativa) contains seven genes encoding polyamine oxidases (PAOs), termed OsPAO1 to OsPAO7, based on their chromosomal number and gene ID number. We previously showed that three of these members, OsPAO3, OsPAO4 and OsPAO5, are abundantly expressed, that their products localize to peroxisomes and that they catalyze the polyamine back-conversion reaction. Here, we have focused on OsPAO1. The OsPAO1 gene product shares a high level of identity with those of Arabidopsis PAO5 and Brassica juncea PAO. Expression of OsPAO1 appears to be quite low under physiological conditions, but is markedly induced in rice roots by spermine (Spm) or T-Spm treatment. Consistent with the above finding, the recombinant OsPAO1 prefers T-Spm as a substrate at pH 6.0 and Spm at pH 8.5 and, in both cases, back-converts these tetraamines to spermidine, but not to putrescine. OsPAO1 localizes to the cytoplasm of onion epidermal cells. Differing in subcellular localization, four out of seven rice PAOs, OsPAO1, OsPAO3, OsPAO4 and OsPAO5, catalyze back-conversion reactions of PAs. Based on the results, we discuss the catabolic path(s) of PAs in rice plant.
KeywordsBack-conversion Oryza sativa OsPAO1 Polyamine Polyamine oxidase Thermospermine
We gratefully acknowledge Drs. M. Yano, M. Teranishi and J. Hidema for providing plasmids and bacterial strains. This study was supported by the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT) to TK (21380063) and to DWK (25·5682, Grant-in-Aid for Young Scientists) and grants from The Saito Gratitude Foundation and The Japan Science Society (The Sasagawa Scientific Research Grant) to DWK. TL was financially supported by the China Scholarship Council.
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