Genome-Wide Identification of Superfamily Genes in and Expression Analysis under Cold Stress.

has strong freezing resistance, surviving temperatures as low as -40 °C, making it an important freeze tolerant germplasm resource of the genus . APETALA2/ethylene responsive factor (AP2/ERF) is a plant-specific superfamily of transcription factors that regulates plant development, growth, and the response to biotic and abiotic stress. In this study, phylogenetic analysis was used to identify 184 genes in the genome, which were classified into five subfamilies (, , , , and ). A significant amount of discordance was observed in the 184 genes distribution of throughout its 16 chromosomes. Duplication was found in 14 tandem and 122 segmental gene pairs, which indicated that duplications may be the main reason for family expansion. Gene structural analysis revealed that 64 genes contained introns. Gene evolution analysis among Juglandaceae revealed that is separated by 14.23 and 15 Mya from and , respectively. Based on promoter analysis in , many cis-acting elements were discovered that are related to light, hormones, tissues, and stress response processes. Proteins that may contribute to cold resistance were selected for further analysis and were used to construct a cold regulatory network based on GO annotation and JmAP2/ERF protein interaction network analysis. Expression profiling using qRT-PCR showed that 14 genes were involved in cold resistance, and that seven and five genes were significantly upregulated under cold stress in female flower buds and phloem tissues, respectively. This study provides new light on the role of the gene in cold stress response, paving the way for further functional validation of TFs and their application in the genetic improvement of and other tree species.