Summary: Rice P1B-Type Heavy-Metal ATPase, OsHMA9, Is a Metal
Sichul Lee, Yu-Young Kim, Youngsook Lee, and Gynheung An*
Division of Molecular and Life Science, Biotechnology Research Center, Pohang University of Science and
Technology, Pohang 790784, Korea
P1B-type heavy-metal ATPases (HMAs) are transmembrane metal-transporting proteins that play a key role in metal homeo-
stasis. Despite their importance, very little is known about their functions in monocot species. We report the characterization of
rice (Oryza sativa) OsHMA9, a member of the P1B-type ATPase family. Semiquantitative reverse transcription-polymerase chain
reaction analyses of seedlings showed that OsHMA9 expression was induced by a high concentration of copper (Cu), zinc (Zn),
and cadmium. We also determined, through promoterTb-glucuronidase analysis, that the main expression was in the vascular
bundles and anthers. The OsHMA9:green fluorescence protein fusion was localized to the plasma membrane. Heterologous
expression of OsHMA9 partially rescued the Cu sensitivity of the Escherichia coli copA mutant, which is defective in
Cu-transporting ATPases. It did not rescue the Zn sensitivity of the zntA mutant, which is defective in Zn-transporting ATPase.
To further elucidate the functional roles of OsHMA9, we isolated two independent null alleles, oshma9-1 and oshma9-2, from the
T-DNA insertion population. Mutant plants exhibited the phenotype of increased sensitivity to elevated levels of Cu, Zn, and
lead. These results support a role for OsHMA9 in Cu, Zn, and lead efflux from the cells. This article is the first report on the
functional characterization of a P1B-type metal efflux transporter in monocots.
A number of heavy metals, including copper (Cu),
zinc (Zn), manganese, and iron, are essential micro-
nutrients for a wide variety of physical processes.