Genome-Wide Identification and Expression Analysis of HD-ZIP I Gene Subfamily in Nicotiana tabacum.

The homeodomain-leucine zipper (HD-Zip) gene family, whose members play vital roles in plant growth and development, and participate in responding to various stresses, is an important class of transcription factors currently only found in plants. Although the HD-Zip gene family, especially the HD-Zip I subfamily, has been extensively studied in many plant species, the systematic report on HD-Zip I subfamily in cultivated tobacco () is lacking. In this study, 39 HD-Zip I genes were systematically identified in (Nt). Interestingly, that 64.5% of the 31 genes with definite chromosome location information were found to originate from N. tomentosoformis, one of the two ancestral species of allotetraploid N. tabacum. Phylogenetic analysis divided the Nt I subfamily into eight clades. Analysis of gene structures showed that Nt I proteins contained conserved homeodomain and leucine-zipper domains. Three-dimensional structure analysis revealed that most I proteins in each clade, except for those in clade η, share a similar structure to their counterparts in . Prediction of cis-regulatory elements showed that a number of elements responding to abscisic acid and different abiotic stresses, including low temperature, drought, and salinity, existed in the promoter region of Nt I genes. The prediction of ortholog-based protein-protein interaction network implied that Nt I proteins have complex connections. The expression profile of these genes showed that different Nt I genes were highly expressed in different tissues and could respond to abscisic acid and low-temperature treatments. Our study provides insights into the evolution and expression patterns of Nt I genes in and will be useful for further functional characterization of Nt I genes in the future.