Functional analysis of the C-terminal region of the vacuolar cadmium-transporting rice OsHMA3.

Rice OsHMA3 is a vacuolar cadmium (Cd) transporter belonging to the P1B-ATPase family and has a long (273aa) C-terminal region. We analyzed the function of the region related to Cd using the transgenic Arabidopsis Col-0 ecotype, which is sensitive to Cd. The OsHMA3 variant containing a truncated (58aa) C-terminal region did not confer Cd tolerance, whereas an OsHMA3 variant containing a longer truncated (105aa) C-terminal region conferred Cd tolerance to transgenic Arabidopsis. We conclude that the C-terminal region, particularly the region containing the first 105aa, has an important role in OsHMA3 activity.

OsHMA3, a P1B-type of ATPase affects root-to-shoot cadmium translocation in rice by mediating efflux into vacuoles.

• The cadmium (Cd) over-accumulating rice (Oryza sativa) cv Cho-Ko-Koku was previously shown to have an enhanced rate of root-to-shoot Cd translocation. This trait is controlled by a single recessive allele located at qCdT7. • In this study, using positional cloning and transgenic strategies, heavy metal ATPase 3 (OsHMA3) was identified as the gene that controls root-to-shoot Cd translocation rates. The subcellular localization and Cd-transporting activity of the gene products were also investigated. • The allele of OsHMA3 that confers high root-to-shoot Cd translocation rates (OsHMA3mc) encodes a defective P(1B) -ATPase transporter. OsHMA3 fused to green fluorescent protein was localized to vacuolar membranes in plants and yeast. An OsHMA3 transgene complemented Cd sensitivity in a yeast mutant that lacks the ability to transport Cd into vacuoles. By contrast, OsHMA3mc did not complement the Cd sensitivity of this yeast mutant, indicating that the OsHMA3mc transport function was lost. • We propose that the root cell cytoplasm of Cd-overaccumulating rice plants has more Cd available for loading into the xylem as a result of the lack of OsHMA3-mediated transportation of Cd to the vacuoles. This defect results in Cd translocation to the shoots in higher concentrations. These data demonstrate the importance of vacuolar sequestration for Cd accumulation in rice.

A single recessive gene controls cadmium translocation in the cadmium hyperaccumulating rice cultivar Cho-Ko-Koku.

The heavy metal cadmium (Cd) is highly toxic to humans and can enter food chains from contaminated crop fields. Understanding the molecular mechanisms of Cd accumulation in crop species will aid production of safe Cd-free food. Here, we identified a single recessive gene that allowed higher Cd translocation in rice, and also determined the chromosomal location of the gene. The Cd hyperaccumulator rice variety Cho-Ko-Koku showed 3.5-fold greater Cd translocation than the no-accumulating variety Akita 63 under hydroponics. Analysis of an F(2) population derived from these cultivars gave a 1:3 segregation ratio for high:low Cd translocation. This indicates that a single recessive gene controls the high Cd translocation phenotype. A QTL analysis identified a single QTL, qCdT7, located on chromosome 7. On a Cd-contaminated field, Cd accumulation in the F(2) population showed continuous variation with considerable transgression. Three QTLs for Cd accumulation were identified and the peak of the most effective QTL mapped to the same region as qCdT7. Our data indicate that Cd translocation mediated by the gene on qCdT7 plays an important role in Cd accumulation on contaminated soil.