Comparative analysis and expression of Dof genes in Citrus sinensis during fruit development
The DNA-binding One Finger (Dof) proteins are a large group of plant-specific transcription factors (TFs) that participate in several biological processes in plants. Although the Dof gene family has been studied in many plant species, detailed information on these genes and their fruit-specific expression during fruit development are not yet available in sweet orange (Citrus sinensis L. Osbeck). Here, we identified and characterized 24 CsDof genes in C. sinensis genome. Phylogenetic analysis showed that orange Dof proteins clustered into four major groups (A, B, C and D) and nine subgroups (A, B1, B2, C1, C2.1, C2.2, C3, D1, D2) based on the established Arabidopsis thaliana classification. The predicted CsDof genes could be mapped on all chromosomes, except for chromosomes 4 and 9. Most of these genes lacked introns or possessed just one intron. Based on freely RNA-seq data, 12 CsDofs with higher transcript abundance in fruits were selected for further analysis by semi-quantitative RT-PCR. This analysis revealed that the CsDof genes exhibit a variety of expression patterns during the early stages of fruit development (up to 90 days after anthesis), making it possible to establish three groups regarding their transcriptional activity. Among them, the CsDof17 showed the highest expression in all sampling stages investigated, indicating that this isoform may play an important role in regulating the early development of sweet orange fruits. Our results provide some useful information for the utilization of the CsDof genes for crop improvement of this important fruit species.