Genome-wide identification of the CmHDZ gene family in Chinese chestnut (Castanea mollissima) and analysis of their expression patterns under different types of abiotic stress

The members of the homologous homeodomain-leucine zipper (HDZ) family of transcription factors play important roles in the ability of plants to cope with adverse conditions. In this study, we analyzed the genome of the Chinese chestnut (Castanea mollissima) to identify the CmHDZ genes involved in stress response. In total, 25 CmHDZ genes were identified, of which 24 were distributed across 12 chromosomes. Evolutionary analysis indicated that the 25 CmHDZ genes were divided into four subfamilies: HDZ I, II, III, and IV, comprising 13, 7, 4, and 1 members, respectively. All CmHDZ protein sequences contained highly conserved homeodomains (motif1). Subcellular localization prediction indicated that most of the CmHDZ members were localized to the nucleus, except for CmHDZ13, which was localized to the chloroplast. Further experiments confirmed the nuclear localization of CmHDZ15. Collinearity analysis revealed that 12 CmHDZ members formed eight pairs of homologous genes. Chinese chestnut shared the least number of gene pairs with rice and maize (10 and 9, respectively) and the highest number with Arabidopsis thaliana (up to 34 pairs). Cis-acting element prediction analysis indicated that the promoters of all 25 CmHDZ genes contained hormone and stress response elements. Moreover, the tissue-specific expression patterns of the CmHDZ genes varied under different types of stress. In particular, the CmHDZ15 expression level changed significantly in response to shading, low-temperature, and high-temperature treatments. The quantitative analysis results confirmed the reliability of the transcriptome data. This study provides a genetic resource for screening resistance genes and for the molecular breeding of Chinese chestnuts.