Functional analysis of <Emphasis Type="Italic">OsPUT1</Emphasis>, a rice polyamine uptake transporter |
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Authors: | Vaishali Mulangi Vipaporn Phuntumart Mustapha Aouida Dindial Ramotar Paul Morris |
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Institution: | (1) Department of Biological Sciences, Bowling Green State University, 442, Life Sciences Building, Bowling Green, OH 43403-09, USA;(2) Maisonneuve-Rosemont Hospital, Research Center, 5415, Boul. de l’Assomption, Montreal, QC, H1T 2M4, Canada; |
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Abstract: | Polyamines are nitrogenous compounds found in all eukaryotic and prokaryotic cells and absolutely essential for cell viability.
In plants, they regulate several growth and developmental processes and the levels of polyamines are also correlated with
the plant responses to various biotic and abiotic stresses. In plant cells, polyamines are synthesized in plastids and cytosol.
This biosynthetic compartmentation indicates that the specific transporters are essential to transport polyamines between
the cellular compartments. In the present study, a phylogenetic analysis was used to identify candidate polyamine transporters
in rice. A full-length cDNA rice clone AK068055 was heterologously expressed in the Saccharomyces cerevisiae spermidine uptake mutant, agp2∆. Radiological uptake and competitive inhibition studies with putrescine indicated that rice gene encodes a protein that
functioned as a spermidine-preferential transporter. In competition experiments with several amino acids at 25-fold higher
levels than spermidine, only methionine, asparagine, and glutamine were effective in reducing uptake of spermidine to 60%
of control rates. Based on those observations, this rice gene was named polyamine uptake transporter 1 (OsPUT1). Tissue-specific expression of OsPUT1 by semiquantitative RT-PCR showed that the gene was expressed in all tissues except seeds and roots. Transient expression
assays in onion epidermal cells and rice protoplasts failed to localize to a cellular compartment. The characterization of
the first plant polyamine transporter sets the stage for a systems approach that can be used to build a model to fully define
how the biosynthesis, degradation, and transport of polyamines in plants mediate developmental and biotic responses. |
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