Abstract
Excessive cadmium (Cd) accumulation in grains of rice (Oryza sativa L.) is a risk to food security. The transporters in the nodes of rice are involved in the distribution of mineral elements including toxic elements to different tissues such as grains. However, the mechanism of Cd accumulation in grains is largely unknown. Here, we report a node-expressed transporter gene, OsCCX2, a putative cation/calcium (Ca) exchanger, mediating Cd accumulation in the grains of rice. Knockout of OsCCX2 caused a remarkable reduction of Cd content in the grains. Further study showed that disruption of this gene led to a reduced root-to-shoot translocation ratio of Cd. Moreover, Cd distribution was also disturbed in different levels of internode and leaf. OsCCX2 is localized to plasma membrane, and OsCCX2 is mainly expressed in xylem region of vascular tissues at the nodes. OsCCX2 might function as an efflux transporter, responsible for Cd loading into xylem vessels. Therefore, our finding revealed a novel Cd transporter involved in grain Cd accumulation, possibly via a Ca transport pathway in the nodes of rice.
Highlights
Cadmium (Cd) is a very toxic heavy metal element and is harmful to humans’ health, when accumulated in the body
For Cd content analysis, the BY4741 transformants expressing pYES2-OsCCX2 or empty vector pYES2 were grown in synthetic Cd-containing drop-out (SG)-Ura liquid medium containing 1, 2, 5, and 10 μM CdCl2 to the log phase, the cells were collected by centrifugation, and washed three times with deionized water
Paraffin section analysis revealed that GUS activity is mainly localized in the parenchyma cells of the vascular tissues including enlarged vascular bundles (EVBs) and diffuse vascular bundles (DVBs) in the node (Figure 1D and Supplementary Figure S1)
Summary
Cadmium (Cd) is a very toxic heavy metal element and is harmful to humans’ health, when accumulated in the body. OsZIP3 functions as a Zn transporter in the node, responsible for controlling the allocation of Zn to the developing tissues in rice (Sasaki et al, 2015) Suppressed expression of this gene resulted in decreased Zn levels in shoot meristem and elongation zone, but elevated Zn accumulation in mature leaves in the RNAi plant. Both OsHMA2 mutant and overexpression plants result in reduction of Cd in the leaves (Satoh-Nagasawa et al, 2012; Takahashi et al, 2012a; Yamaji et al, 2013) Another transporter, OsLCT1, has been shown to mediate phloem Cd transport in nodes and leaf blades of rice. OsCCX2 is localized in plasma membrane and plays a role at the nodes in mediating Cd translocation and distribution
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
