Os07g0232900

The rice Os07g0232900 was reported as Heavy metal ATPases 3 (OsHMA3) four times in 2010 and 2011 by researchers from Japan.

Annotated Information

Function

Figure 1. Mutant VS. WT(from reference) .
(C and D) shows a Complementation test. Cd concentration in the shoots (C) and roots (D) of three independent transgenic lines carrying OsHMA3 and empty vector in Anjana Dhan background. (E and F) shows the Effect of decreased expression of OsHMA3 on Cd accumulation. Cd concentration in the shoots (E) and roots (F) of three independent RNAi lines and vector control plants in Nipponbare background.

Figure 2. Complementary Test of OsHMA3 in S. cerevisiae(Yeast)

Figure 3. Phylogenetic relationship of HMA proteins in rice (black), Arabidopsis thaliana (blue), and Arabidopsis halleri (green)(from reference) .

• OsHAM3 encodes a P1B-type ATPase, acting as a Cd transporter, which can control the ability of root-to-shoot Cd translocation. This gene is involved in the efflux of divalent metal ions across a vacuole membrane.
• Defective function of OsHAM3 leads to high Cd accumulation in 3 different rice cultivars: Cho-Ko-Koku, Anjana Dhan as well as Jarjan, while the rice cultivar Nipponbare with intact function of OsHAM3 gets low accumulation rate of Cd.
• OsHMA3 from the low Cd-accumulating cultivar limits the translocation of Cd from the roots to the above-ground tissues by selectively sequestrating Cd into the root vacuoles, thus decrease the accumulation rate of Cd in the whole plant.
• In contrast, the allelic gene OsHMA3mc from the high Cd-accumulating cultivar lost the function to act as a firewall of Cd because of a single amino acid mutation.The study of this gene will be of great value for phytoremediation of Cd-polluted paddy Welds.

GO assignment(s): GO:0003824, GO:0006812, GO:0008152, GO:0016020, GO:0016021, GO:0030001, GO:0046872, GO:0046873

Wild Type & Mutations

Cd Accumulation Rates in different Rice plants, counted by Daisei Uenoa et al.

• Analysis with three independent transgenic lines showed that introduction of OsHMA3 from Nipponbare into Anjana Dhan resulted in decreased Cd accumulation in the shoots (P < 0.01) (Fig 1C), but increased Cd accumulation in the roots (P<0.01) (Fig 1D).
• Furthermore, when OsHMA3 expression was knocked down in Nipponbare by RNAi, the concentration of Cd in the shoot was increased by 2.1- to 2.5-times in the RNAi lines compared with the empty-vector control plants (P < 0.05) (Fig. 1E) and the root Cd concentration was decreased by 74 to 60% in the RNAi line (P < 0.05) (Fig 1F).
  

Complementary Test of OsHMA3 in S. cerevisiae(Yeast) by Hidenori Miyadate et al.

• The wild-type yeast strain (BY4743) can grow, with only slight inhibition, in media containing up to 60 μM of CdCl2. The mutant strain (YDR135c), which lacks Cd transport to the vacuole, shows severe growth inhibition above 30 μM CdCl2(Fig 2).
• Expression of OsHMA3 in the mutant yeast strain increased its Cd tolerance(YDR135c-A63) so that its level of tolerance was only slightly inferior to that of the wild strain. By contrast, mutant yeast expressing OsHMA3mc did not grow at 30 μM CdCl2('YDR135c-A63-CKK), indicating that OsHMA3mc had no effect on Cd sensitivity in YDR135c(Fig 2).

Expression Pattern

• RT-PCR analysis by Hidenori Miyadate et al. showed that the expression level of OsHMA3 was higher in the roots than in the leaves of Akita 63 and Cho-Ko-Koku seedlings grown in hydroponic culture containing 5 μg/L of CdCl2 for 14 d.
  
  
• RT-PCR analysis by Daisei Uenoa et al. showed that OsHMA3 is mainly expressed in the roots at a similar level in Nipponbare and Anjana Dhan contrasting in Cd accumulation. Their Spatial analysis shows that there is no difference in the expression of OsHMA3 among different root segments: 0 to 1 cm, 1 to 2 cm, and 2 to 3 cm from the apex of both cultivars..

Localization

Cellular and Subcellular Localization analysis by Hidenori Miyadate et al. and Daisei Ueno et al. showed that OsHMA3 is localized at the vacuolar membrane of all root cells in rice.

Evolution

Phylogenetic analysis by Daisei Uenoa et al. shows that the amino acid sequence similarity of OsHMA3 to HMA3 proteins from other plants is very low, with 39.4% identity to the closest homolog in Arabidopsis (AtHMA3 from ecotype Wassilewskija) and AhHMA3 from Arabidopsis halleri, a Zn-hyperaccumulating plant(Fig 3) .

Knowledge Extension

• Cadmium (Cd) is a highly toxic heavy metal for all organisms. In humans, Cd exposure has been associated with cancers of the prostate, lungs, and testes, kidney tubule damages, rhinitis, emphysema, osteomalacia, and bone fractures (1, 2). Cd also inhibits plant growth and development by binding to free sulfhydryl residues and interfering with homeostasis of essential elements, such as zinc, calcium, and iron, or causing their displacement from proteins.
  
  

• There has been an increasing interest in the use of hyperaccumulator plants to remediate Cd-contaminated soils. The hyperaccumulator plants reduce the soil Cd content by translocation and accumulating high concentrations of the heavy metal in their shoots. In the last decade, several plant species were identified as Cd hyperaccumulators, including Noccaea (Thlaspi) caerulescens, Arabidopsis halleri, Thlaspi praecox, and Sedum alfredii).

Labs working on this gene

• Laboratory of Plant Genetics and Breeding, Department of Biological Production, Faculty of Bioresource Sciences, Akita Prefectural University, Kaidoubata-Nishi 241-438, Shimoshinjyo-Nakano, Akita 010-0195, Japan
• Akita Agricultural Experiment Station, Genpachizawa 34-1, Aikawa, Yuwa, Akita 010-1231, Japan
• Department of Paddy Farming, National Agricultural Research Center for Tohoku Region, Yotsuya, Daisen 014-0102, Japan
• Graduate School of Life and Environmental Sciences, University of Tsukuba, Tennoudai 1-1-1, Tsukuba, 305-8572 Ibaraki, Japan
• Institute of Plant Science and Resources, Okayama University, Chuo 2-20-1, Kurashiki 710-0046, Japan