Dual-function DEFENSIN 8 mediates phloem cadmium unloading and accumulation in rice grains

文献类型： 外文期刊

第一作者： Gu, Tian-Yu

作者： Gu, Tian-Yu;Qi, Zi-Ai;Chen, Si-Ying;Yan, Jing;Fang, Zi-Jun;Gong, Ji-Ming;Gu, Tian-Yu;Gong, Ji-Ming;Gu, Tian-Yu;Qi, Zi-Ai;Chen, Si-Ying;Gong, Ji-Ming;Yan, Jing;Wang, Jun-Min

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期刊名称：PLANT PHYSIOLOGY （ 影响因子：8.005； 五年影响因子：9.115 ）

ISSN： 0032-0889

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收录情况： SCI

摘要： The defensin family member DEFENSIN 8 (DEF8) mediates both xylem cadmium (Cd) loading and phloem Cd unloading via the chelation and secretion mechanism in rice. Grain cadmium (Cd) is translocated from source to sink tissues exclusively via phloem, though the phloem Cd unloading transporter has not been identified yet. Here, we isolated and functionally characterized a defensin-like gene DEFENSIN 8 (DEF8) highly expressed in rice (Oryza sativa) grains and induced by Cd exposure in seedling roots. Histochemical analysis and subcellular localization detected DEF8 expression preferentially in pericycle cells and phloem of seedling roots, as well as in phloem of grain vasculatures. Further analysis demonstrated that DEF8 is secreted into extracellular spaces possibly by vesicle trafficking. DEF8 bound to Cd in vitro, and Cd efflux from protoplasts as well as loading into xylem vessels decreased in the def8 mutant seedlings compared with the wild type. At maturity, significantly less Cd accumulation was observed in the mutant grains. These results suggest that DEF8 is a dual function protein that facilitates Cd loading into xylem and unloading from phloem, thus mediating Cd translocation from roots to shoots and further allocation to grains, representing a phloem Cd unloading regulator. Moreover, essential mineral nutrient accumulation as well as important agronomic traits were not affected in the def8 mutants, suggesting DEF8 is an ideal target for breeding low grain Cd rice.

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