Genome-wide identification and expression analysis of the Dof gene family reveals their involvement in hormone response and abiotic stresses in sunflower (Helianthus annuus L.)

DNA binding with one finger (Dof), plant-specific zinc finger transcription factors, can participate in a variety of physiological and biochemical processes during plant life. As one of the most important oil crops in the world, Sunflower (Helianthus annuus L.) has important economic and ornamental values. However, systematic analysis of H. annuus Dof (HaDof) members and their functions has not been conducted extensively. In this study, we identified 50 HaDof genes, which distributed unevenly on 17 chromosomes of sunflower. A comprehensive overview of the HaDof genes is presented, including the chromosome locations, phylogenetic analysis, and expression profile characterization. Phylogenetic analysis of the 366 Dof members identified from 11 species showed that four groups (further subdivided into nine subfamilies) were classified. Segmental duplications are predominant for the expansion of sunflower Dof genes, and all the segmental duplicate gene pairs are under purifying selection due to strong evolutionary constraints. Furthermore, the HaDof genes displayed differential expression in normal tissues, under hormone treatment or abiotic stress by analyzing RNA-seq data from previous studies and RT-qPCR data in current study. The expression of HaDof04 and HaDof43 were not detected in any samples, which implies that they may gradually enter the process of pseudogenization. Some HaDof genes, such as HaDof25 and HaDof30, can respond to exogenous plant hormones, such as kinetin, brassinosteroid, auxin or strigolactone. HaDof15 and HaDof35 may participate in the abiotic stress resistance of sunflower seedling. Our study is the first step towards the phylogeny and abiotic stress response of sunflower Dof family genes, and may provide useful reference information for functional studies on hormone response, abiotic stress resistance and molecular breeding in sunflower and other species.