The Functional Analysis Of Zinc-Iron Transporter Family Member OsZIP9 In Rice

Zinc（Zn）is one of the essential trace elements for plant growth and development,which plays an important role in diverse biochemical processes.Zinc deficiency will have a negative impact on the physiological activities of plants,while excessive zinc will be toxiced to plants.ZRT,IRT-like protein（ZIP）is an important protein to maintain zinc-iron balance in plants.In this study,OsZIP9,a member of zinc-iron transport protein family,was studied to analyze its function in the process of zinc ion absorption and transport and provide molecular basis and theoretical basis for cultivating zinc-rich rice.The main results are as follows:1.There are 16 transporters in ZIP family,which are distributed on rice chromosomes 1-8.OsZIP9 protein has 8 transmembrane domains,which are similar to other ZIP proteins.2.ZIP family genes（except OsIRT2 and OsZIP16）were expressed in zinc uptake deficient yeast strain ZHY3（zrt1zrt2）.The results showed that the expression of OsIRT1,OsZIP3-OsZIP10 and OsZIP14 could effectively compensate for the sensitive growth defect of zinc uptake deficient yeast to zinc deficiency,indicating that these genes had Zn²⁺transport activity.The Zn²⁺transport activity of OsZIP9 was significantly higher than that of all other ZIP members.3.qRT-PCR results showed that OsZIP9 was specifically expressed in roots and regulated by Zn concentration.Zinc deficiency induced OsZIP9 expression up-regulation,while excessive zinc inhibited OsZIP9 expression.Based on the GUS staining results showed that OsZIP9 was specifically expressed in the exocortex and epidermal cells of lateral roots.In addition,the results of subcellular localization showed that OsZIP9 was located in the plasma membrane.4.The growth of oszip9 mutant plants was significantly weaker than that of the wild type seriously under low concentration zinc treatment,and the zinc content in the root and aboveground part of the oszip9 mutant was significantly lower than that of the wild type;Under high concentration zinc treatment,the growth of oszip9 mutant plants was not significantly different from that of the wild type,but the zinc concentration in roots of oszip9 mutant plants was still lower than that of wild type;Under the condition of normal zinc in the field,,the zinc concentration of straw and grains in oszip9 mutant plants was significantly lower than that of wild type.5.In the hydroponic culture experiments of all zinc concentration treatments,there was no significant difference in plant height between OsZIP9 overexpression plants and wild type,but the zinc concentration in shoot and root was significantly higher than that in wild type.In normal zinc environment,zinc homeostasis in plants was destroyed due to overexpression of OsZIP9,and zinc concentration in straw and grain was significantly lower than that in wild type.To sum up,we found that OsZIP9 is a transporter in the process of zinc uptake in rice,and its zinc transport activity is significantly higher than that of other ZIP members,and is specifically expressed in the outer cortex of lateral roots.The knockout of this gene will significantly reduce the ability of rice to accumulate zinc.