Genome-Wide Identification of the DOF Gene Family in Kiwifruit ( Actinidia chinensis ) and Functional Validation of AcDOF22 in Response to Drought Stress.

DNA-binding one zinc finger (DOF) transcription factors are crucial plant-specific regulators involved in growth, development, signal transduction, and abiotic stress response generation. However, the genome-wide identification and characterization of AcDOF genes and their regulatory elements in kiwifruit ( Actinidia chinensis ) has not been thoroughly investigated. In this study, we screened the kiwifruit genome database and identified 42 AcDOF genes ( AcDOF1 to AcDOF42 ). Phylogenetic analysis facilitated the categorization of these genes into five subfamilies ( DOF -a, DOF -b, DOF -c, DOF -d, and DOF -e). We further analyzed the motifs, conserved domains, gene structures, and collinearity of the AcDOF gene family. Gene ontology (GO) enrichment analysis indicated significant enrichment in the "flower development" term and the "response to abiotic stress" category. Promoter prediction analysis revealed numerous cis-regulatory elements related to responses to light, hormones, and low-temperature and drought stress in AcDOF promoters. RNA-seq expression profiles demonstrated the tissue-specific expression of AcDOF genes. Quantitative real-time PCR results showed that six selected genes ( AcDOF04 , AcDOF09 , AcDOF11 , AcDOF13 , AcDOF21 , and AcDOF22 ) were differentially induced by abscisic acid (ABA), methyl jasmonate (MeJA), and cold, salt, and drought stresses, with AcDOF22 specifically expressed at high levels in drought-tolerant cultivars. Further experiments indicated that transient AcDOF22 overexpression in kiwifruit leaf disks reduced water loss and chlorophyll degradation. Additionally, AcDOF22 was localized to the nucleus and exhibited transcriptional activation, enhancing drought resistance by activating the downstream drought marker gene AcDREB2A . These findings lay the foundation for elucidating the molecular mechanisms of drought resistance in kiwifruit and offer new insights into drought-resistant breeding.