Identification of bZIP gene family and screening of selenium metabolism-related candidate genes in Broussonetia papyrifera L.

【Objective】 To identify and analyze the members of bZIP（basic leucine zipper） gene family members in Broussonetia papyrifera L.,and screen the key genes involved in selenium metabolism in B. papyrifera,which could provide theoretical reference for further study of the biological function mechanism of B. papyrifera bZIP gene family and its role in selenium metabolism. 【Method】 Based on the complete genome data of B. papyrifera,bioinformatics methods were used to identify the members of the bZIP gene family in B. papyrifera. The analysis included studying their gene structure,promoter cis-elements,protein systematic evolution relationships,and the transient transformation of tobacco leaves mediated by Agrobacterium tumefaciens was used for protein subcellular localization. The expression levels of B. papyrifera bZIP family genes under different selenium sources and concentrations were analyzed by transcriptome sequencing（RNASeq） and real-time fluorescence quantitative PCR.【Result】A total of 38 bZIP gene family members were identified（BpbZIP01-BpbZIP38）,with number of amino acids encoded ranging from 140 to 894 amino acids,relative molecular weights ranging from 16357.39 to 96969.63 Da,theoretical isoelectric points ranging from 5.24 to 9.76,all of which were hydrophilic proteins,and instability coefficients ranging from 52.54 to 73.89. Among them,36 BpbZIPs were localized in the nucleus,while BpbZIP15 and BpbZIP19 were localized in the peroxisome and endoplasmic reticulum respectively.Based on the phylogenetic tree,the BpbZIPs proteins were divided into 10 subfamilies. The number of BpbZIPs proteins in each subfamily was 6（subfamily A）, 1（subfamily B）, 1（subfamily C）, 7（subfamily D）, 2（subfamily E）, 1（subfamily F）, 4（subfamily G）, 2（subfamily H）, 6（subfamily I） and 8（subfamily S）. In each subfamily, most BpbZIPs proteins and the bZIP protein of the mulberry tree were clustered into a branch. The number of exons of different BpbZIPs genes varied greatly, ranging from 1 to 16, but the gene length and structure of the same subfamily had certain similarities. BpbZIPs gene promoters contained various response elements such as light response,hormone response and stress response. Under different concentrations of sodium selenate and sodium selenite treatments,except for BpbZIP17,all BpbZIPs genes responded to selenium treatment by up-regulation or down-regulation. The results of correlation analysis and real-time fluorescence quantitative PCR showed that the expression levels of BpbZIP04 and BpbZIP05 genes were closely related to the total selenium content after sodium selenite and sodium selenate treatments. 【Conclusion】 Members of the bZIP gene family of B. papyrifera are involved in various biological and non-biological stresses. BpbZIP04 and BpbZIP05genes play important roles in selenium metabolism and tolerance in B. papyrifera.