Abstract
Growth regulatory factors (GRFs) are sequence-specific DNA-binding transcription factors that play pivotal roles in regulating plant growth and development, and in enhancing plant tolerance to biotic and abiotic stresses. Although genome-wide structural and evolutionary studies have mapped and analyzed GRF genes in different plant species, knowledge of their characteristics and functions in sunflower (Helianthus annuus) remains limited. In this study, we used bioinformatics analyses and transgenic experiments to systematically analyze the structure and function of these genes. A total of 17 HaGRF genes were identified and classified into four distinct clades, with members of the same clade sharing conserved exon-intron structures and domain architectures. All HaGRFs were predicted to localize to the nucleus, which was experimentally verified for HaGRF2c, HaGRF3, and HaGRF8c. Transcriptome analysis demonstrated tissue-specific expression and stress-responsive profiles among the HaGRF genes. Quantitative real-time PCR revealed that several HaGRF genes were significantly induced under polyethylene glycol and NaCl stress. Additionally, ectopic expression of HaGRF2c in Arabidopsis enhanced growth and conferred greater drought tolerance, supporting its dual functions in regulating growth and in adapting to stress. In summary, this research elucidates the evolutionary relationships, conserved structural characteristics, expression patterns, and roles of the HaGRF gene family in sunflowers. These findings not only deepen our understanding of the biological functions of GRF transcription factors in sunflowers but also provide valuable candidate genes for improving yield and stress resistance in H. annuus.