Zinc transporters for uptake, translocation and distribution in rice

Jian Feng Maa, N. Yamajia and A. Sasakia

a Institute of Plant Science and Resources, Okayama University, Japan

maj@okayama-u.ac.jp

Zinc (Zn) is an essential micronutrient for plant growth and development. Especially, developing tissues such as meristem require high Zn for their active growth. In my talk, I will introduce transporters involved in uptake, root-to-shoot translocation and distribution of Zn in rice. OsZIP9, a member of ZIP family is mainly expressed at the exodermis of the roots. Its expression was up-regulated by Zn-deficiency. Knockdown of this gene resulted in decreased Zn uptake and growth. Therefore, OsZIP9 is a transporter for Zn uptake under Zn-deficient condition. After uptake, part of Zn will be sequestered to the vacuoles by OsHMA3, a member of HMA family. Our recent work showed that OsHMA3 plays an important role in both Zn detoxification and storage in rice roots. The root-to-shoot translocation of Zn is mediated by OsHMA2, a homolog of OsHMA3. OsHMA2 is localized to the plasma membrane of root pericyclic cells. Knockout of this gene resulted in decreased translocation of Zn to the shoots. Distribution of Zn to different organs of above-ground part is mediated by at least two transporters, OsZIP3 and OsHMA2. Both OsZIP3 and OsHMA2 are highly expressed in the nodes, a hub for mineral element distribution in rice. OsZIP3 is localized in the xylem intervening parenchyma cells and xylem transfer cells of enlarged vascular bundles (EVBs), while OsHMA2 is localized at phloem region of both EVBs and diffuse vascular bundles (DVBs). Therefore, OsZIP3 is responsible for unloading Zn from the xylem of EVB, while OsHMA2 is responsible for loading Zn to the phloem of DVBs and EVBs. Knockout of either OsHMA2 or OsZIP3 resulted in decreased distribution of Zn to the developing tissues.

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