OsbZIP48,A Regulator Of Zinc Homeostasis In Rice

Zinc(Zn)is an essential microelement in plants.It plays an important role in the growth and development of plants as a main component of proteins.Both Zn deficiency and over-accumulation adversely affects plant growth.Therefore the Zn level in plants is strictly controled.In the rice genome,OsbZIP48 is a homologous protein of AtbZIP19 and AtbZIP23 in Arabidopsis thaliana.Analysis of protein structure showed that OsbZIP48 was a classical bZIP transcription factor.It has a bZIP domain which consists of a basic domain and eight leucine zipper.It was showed that OsbZIP48 had a strong transcriptional activity in yeast single miscellaneous experiments.The subcellular localization of OsbZIP48-GFP in protoplasts of rice revealed that OsbZIP48 mainly localized in nuclear.In order to fiurther explore the biological function of OsbZIP48,osbzip48(1)-1,osbzip48(1)-3 and osbzip48(2)-1,three mutant lines and 16 overexpression lines of osbZIP48 were got in this study.Results showed that the mutant of OsbZIP48 was sensitive to Zn deficiency(-Zn)and the overexpression of OsbZIP48 increased Zn deficiency tolerance.However,there were no significant differences between mutant and WT under iron,copper and manganese deficiency condition.In order to make sure the phenotype is caused by Zn deficiency,Zn was re-added to mutant and WT grown in Zn deficiency condition for 7 d and results showed that Zn rescue the growth of mutant.At the same time,the content of elements in rice was measured.The results showed that Zn concentration in the shoots and roots of the mutant was significantly high compared with WT under the condition of Zn deficiency,and the increase of Zn in the shoots was mainly accumulated in the base node.There is a large amount of Zn accumulated in the root and basal node of mutant under normal conditions too.Therefore,mutation of OsbZIP48 weakened the transport of Zn from the base node to the shoots,which lead to local Zn deficiency and abnormal growth.In order to explain the phenotype of OsbZIP48 mutants under Zn deficiency condition at the molecular level,RNA-seq analysis was performed in mutants and WT under both Zn-deficiency and Zn-sufficienct conditions.The results showed that mutation of OsbZIP48 led to the expression 99 genes no longer being affected by Zn deficiency,including OsZIP4 and OsZIP8 which involved in Zn transport.Therefore,OsbZIP48 regulates the transport of Zn by regulating the expression of OsZIP4 and OsZIP8.